"sh: 1: file: not found" thrown in Perl – Debian

So this is an issue I see thrown around on several coding help-sites that always have a slight variation. I’m not entirely familiar with what it means, and what’s even more curious is that this error is thrown midway through a larger Upload.pm script, and does not cause any sort of fatal error. It gets tossed into my error log somewhere during this unless conditional snippet

     # If this is the first slice, validate the file extension and mime-type. Mime-type of following slices should be "application/octet-stream".
  unless ( defined $response{'error'} ) {
    if ( $slice->{'index'} == 1 ) {
      my ($filename, $directory, $extension) = fileparse($path.$parent_file, qr/.[^.]*/);

      unless ( is_valid_filetype($slice->{'tmp_file'}, $extension) ) {
        $response{'error'} = "Invalid file type.";
        $response{'retry'} = 0;
      }
    }
  }

Now, let me be perfectly honest. I don’t really understand the error message, and I could really use some help understanding it, as well as solving it.
Our Perl based web app has refused to let us upload files correctly since upgrading to Debian Bullseye, and I’ve been stuck debugging this code I didn’t write for a few days now. I’m wondering if the upgrade depreciated some Perl modules, or if the directories to said modules are no longer working?

I’m testing this in a Ubuntu based Docker environment running Debian Bullseye on an Apache 2 server.

If you need any more context, clarification, etc, please let me know.

is_valid_filetype() looks like this:

sub is_valid_filetype
{
  my ($tmp_file, $extension) = @_;

  if ( $tmp_file && $extension ) {
    # Get temp file's actual mime-type.
    my $mime = qx/file --mime-type -b '${tmp_file}'/;
    $mime =~ s/^s+|s+$//g;

    # Get valid mime-types matching this extension.
    my $dbh = JobTracker::Common::dbh or die("DBH not available.");
    my $mime_types = $dbh->selectrow_array('SELECT `mime_types` FROM `valid_files` WHERE `extension` = ?', undef, substr($extension, 1));

    if ( $mime && $mime_types ) {
      if ( $mime_types !~ /,/ ) {
        # Single valid mime-type for this extension.
        if ( $mime eq $mime_types ) {
          return 1;
        }
      } else {
        # Multiple valid mime-types for this extension.
        my %valid_mimes = map { $_ => 1 } split(/,/, $mime_types);
        if ( defined $valid_mimes{$mime} ) {
          return 1;
        }
      }
    }
  }

  return 0;
}