What is wrong with the BICEP configuration upon deploy with deployment slots in Azure?

I am making a deploy using BICEP and it has been working fine. Though now I need to make use of deployment slots as deployment disturbs our users.

I read the documentation and got it working, at least what I thought. I make a deploy to the staging slot, making a swap and everything works. First time I expect the staging slot to be empty after the deploy but not as I deploy another time. As I do a swap I expect the old production code to be the staging code but it is not. Staging is empty, which is bad as I can’t switch back in case something went wrong with the new code.

After lots of reruns of my deploy I have noticed that the functionapp is emptied of its content as the BICEP is run, not what I expect from what I have read should happen with my configuration.

Is there a misconfiguration somewhere I just can’t see? Something goes wrong BEFORE deploying the content to the Azure Function.

My BICEP (or part of it)

resource sites_azfun_xxxxxxxxxxxxxxx_web 'Microsoft.Web/sites@2022-09-01' = {
  name: sites_azfun_xxxxxxxxxxxxxxx_name
  location: location
  tags: {
    DebitCode: vDebitCode
  }
  kind: 'functionapp'
  identity: {
    type: 'SystemAssigned'
  }
  properties: {
    clientAffinityEnabled: false
    clientCertEnabled: false
    clientCertMode: 'Optional'
    containerSize: 1536
    dailyMemoryTimeQuota: 0
    enabled: true
    hostNamesDisabled: false
    hostNameSslStates: [
      {
        name: '${sites_azfun_xxxxxxxxxxxxxxx_name}.azurewebsites.net'
        sslState: 'Disabled'
        hostType: 'Standard'
      }
      {
        name: '${sites_azfun_xxxxxxxxxxxxxxx_name}.scm.azurewebsites.net'
        sslState: 'Disabled'
        hostType: 'Repository'
      }
    ]
    httpsOnly: true
    hyperV: false
    isXenon: false
    redundancyMode: 'None'
    reserved: false
    scmSiteAlsoStopped: false
    serverFarmId: serverfarms_yyyyyyyyyPlan_name_resource.id
  }
}

resource sites_azfun_xxxxxxxxxxxxxxx_web_config 'Microsoft.Web/sites/config@2022-09-01' = {
  parent: sites_azfun_xxxxxxxxxxxxxxx_web
  name: 'web'
  properties: {
    numberOfWorkers: 1
    defaultDocuments: [
      'Default.htm'
      'Default.html'
      'Default.asp'
      'index.htm'
      'index.html'
      'iisstart.htm'
      'default.aspx'
      'index.php'
    ]
    netFrameworkVersion: 'v7.0'
    phpVersion: '5.6'
    requestTracingEnabled: false
    remoteDebuggingEnabled: false
    httpLoggingEnabled: false
    logsDirectorySizeLimit: 35
    detailedErrorLoggingEnabled: false
    publishingUsername: '$${sites_azfun_xxxxxxxxxxxxxxx_name}'
    scmType: 'None'
    use32BitWorkerProcess: true
    webSocketsEnabled: false
    alwaysOn: bool(always_on)
    managedPipelineMode: 'Integrated'
    virtualApplications: [
      {
        virtualPath: '/'
        physicalPath: 'site\wwwroot'
        preloadEnabled: false
      }
    ]
    loadBalancing: 'LeastRequests'
    experiments: {
      rampUpRules: []
    }
    autoHealEnabled: true
    cors: {
      allowedOrigins: [
        'https://functions.azure.com'
        'https://functions-staging.azure.com'
        'https://functions-next.azure.com'
      ]
      supportCredentials: false
    }
    localMySqlEnabled: false
    ipSecurityRestrictions: [
      {
        ipAddress: '***'
        action: '***'
        priority: 1
        name: '***'
        description: '***'
      }
    ]
    scmIpSecurityRestrictions: [
      {
        ipAddress: '***'
        action: '***'
        priority: 1
        name: '***'
        description: '***'
      }
    ]
    scmIpSecurityRestrictionsUseMain: false
    http20Enabled: false
    minTlsVersion: '1.2'
    ftpsState: 'Disabled'
  }
}

resource sites_azfun_xxxxxxxxxxxxxxx_web_azurewebsites_net 'Microsoft.Web/sites/hostNameBindings@2022-09-01' = {
  parent: sites_azfun_xxxxxxxxxxxxxxx_web
  name: '${sites_azfun_xxxxxxxxxxxxxxx_name}.azurewebsites.net'
  properties: {
    siteName: sites_azfun_xxxxxxxxxxxxxxx_name
    hostNameType: 'Verified'
  }
}

resource sites_azfun_xxxxxxxxxxxxxxx_staging 'Microsoft.Web/sites/slots@2022-09-01' = {
  name: stagingslot_azfun_xxxxxxxxxxxxxxx_name
  parent: sites_azfun_xxxxxxxxxxxxxxx_web
  location: location
  kind: 'functionapp'
  properties: {
    serverFarmId: serverfarms_yyyyyyyyyyPlan_name_resource.id
  }
}

resource sites_azfun_xxxxxxxxxxxxxxx_staging_scm 'Microsoft.Web/sites/slots/basicPublishingCredentialsPolicies@2022-09-01' = {
  parent: sites_azfun_xxxxxxxxxxxxxxx_staging
  name: 'scm'
  properties: {
    allow: true
  }
}

resource sites_azfun_xxxxxxxxxxxxxxx_staging_config 'Microsoft.Web/sites/slots/config@2022-09-01' = {
  parent: sites_azfun_xxxxxxxxxxxxxxx_staging
  name: 'web'
  properties: {
    numberOfWorkers: 1
    defaultDocuments: [
      'Default.htm'
      'Default.html'
      'Default.asp'
      'index.htm'
      'index.html'
      'iisstart.htm'
      'default.aspx'
      'index.php'
    ]
    netFrameworkVersion: 'v7.0'
    phpVersion: '5.6'
    requestTracingEnabled: false
    remoteDebuggingEnabled: false
    httpLoggingEnabled: false
    logsDirectorySizeLimit: 35
    detailedErrorLoggingEnabled: false
    publishingUsername: '$${sites_azfun_xxxxxxxxxxxxxxx_name}__staging'
    scmType: 'None'
    use32BitWorkerProcess: true
    webSocketsEnabled: false
    alwaysOn: bool(always_on)
    managedPipelineMode: 'Integrated'
    virtualApplications: [
      {
        virtualPath: '/'
        physicalPath: 'site\wwwroot'
        preloadEnabled: false
      }
    ]
    loadBalancing: 'LeastRequests'
    experiments: {
      rampUpRules: []
    }
    autoHealEnabled: true
    cors: {
      allowedOrigins: [
        'https://functions.azure.com'
        'https://functions-staging.azure.com'
        'https://functions-next.azure.com'
      ]
      supportCredentials: false
    }
    localMySqlEnabled: false
    ipSecurityRestrictions: [
      {
        ipAddress: '***'
        action: '***'
        priority: 1
        name: '***'
        description: '***'
      }
    ]
    scmIpSecurityRestrictions: [
      {
        ipAddress: '***'
        action: '***'
        priority: 1
        name: '***'
        description: '***'
      }
    ]
    scmIpSecurityRestrictionsUseMain: false
    http20Enabled: false
    minTlsVersion: '1.2'
    ftpsState: 'Disabled'
  }
}

resource sites_azfun_xxxxxxxxxxxxxxx_staging_azurewebsites_net 'Microsoft.Web/sites/slots/hostNameBindings@2022-09-01' = {
  parent: sites_azfun_xxxxxxxxxxxxxxx_staging
  name: '${sites_azfun_xxxxxxxxxxxxxxx_name}-staging.azurewebsites.net'
  properties: {
    siteName: 'azfun-xxxxxxxxxxxxxxx-lab(staging)'
    hostNameType: 'Verified'
  }
}

My azure pipeline, in yml (or part of it)

stages:
- stage: ${{ parameters.environmentName }}
  dependsOn: 
    ${{ parameters.dependsOn }}
  variables:
    - ${{ parameters.varGroups }}
  jobs:
  - deployment: azure_resources
    displayName: "Creating or updating resources"
    environment: ${{ parameters.azureDevopsEnvironmentName }}
    variables: 
      - name: templateFile
        value: 'main.bicep'
      - name: parametersFile
        value: 'main.parameters.json'
      - ${{ parameters.varGroups }}
    condition: succeeded()
    pool:
      vmImage: windows-latest
    strategy:
      runOnce:
        deploy:
          steps:
            - task: replacetokens@5
              name: tokens_in_parameterfile
              displayName: 'Replacing tokens in files'
              inputs:
                targetFiles: |
                  ../BuildPipeline/BICEP/$(parametersFile)
                encoding: 'auto'
                tokenPattern: 'octopus'
                writeBOM: true
                actionOnMissing: 'warn'
                keepToken: false
                actionOnNoFiles: 'continue'
                enableTransforms: false
                enableRecursion: false
                useLegacyPattern: false
                enableTelemetry: false
            - task: AzureResourceManagerTemplateDeployment@3
              name: 'deploy'
              displayName: 'Deploy resources to resource group'
              inputs:
                deploymentName: 'deploy'
                deploymentScope: 'Resource Group'
                azureResourceManagerConnection: $(azuredevops_serviceendpoint_azurerm)
                action: 'Create Or Update Resource Group'
                resourceGroupName: ${{ parameters.resourceGroupName }}-${{ lower(parameters.environmentName) }}
                location: ${{ parameters.location }}
                templateLocation: 'Linked artifact'
                csmFile: '../BuildPipeline/BICEP/$(templateFile)'
                csmParametersFile: '../BuildPipeline/BICEP/$(parametersFile)'
                deploymentMode: 'Incremental'

            - ${{ if eq(parameters.deploy_xxxxxxxxxxxxxxx, true) }}:
              - task:  AzureFunctionApp@2
                name: 'xxxxxxxxxxxxxxx_content'
                displayName: 'Deploy content for xxxxxxxxxxxxxxx'
                inputs:
                  ${{ if eq(lower(parameters.environmentName), 'xxxx') }}:
                    appName: azfun-xxxxxxxxxxxxxxx
                  ${{ else }}:
                    appName: azfun-xxxxxxxxxxxxxxx-${{ lower(parameters.environmentName) }}
                  connectedServiceNameARM: '$(azuredevops_serviceendpoint_azurerm)'
                  appType: 'functionApp'
                  package: '../BuildPipeline/xxxxxxxxxxxxxxx/**/*.zip'
                  deployToSlotOrASE: true
                  resourceGroupName: ${{ parameters.resourceGroupName }}-${{ lower(parameters.environmentName) }}
                  slotName: 'staging'
                  deploymentMethod: 'auto'

              - task: AzureAppServiceManage@0
                displayName: 'Swap content for xxxxxxxxxxxxxxx'
                inputs:
                  azureSubscription: '$(azuredevops_serviceendpoint_azurerm)'
                  ${{ if eq(lower(parameters.environmentName), 'xxxx') }}:
                    WebAppName: azfun-xxxxxxxxxxxxxxx
                  ${{ else }}:
                    WebAppName: azfun-xxxxxxxxxxxxxxx-${{ lower(parameters.environmentName) }}
                  ResourceGroupName: ${{ parameters.resourceGroupName }}-${{ lower(parameters.environmentName) }}
                  SourceSlot: staging
                  SwapWithProduction: true