Laravel model is returning null for belongsTo and hasOne. PhpMyAdmin says "Link not found!", but the key exists and is directly accessible in both

I have two models named: Subject and Group, Subject has a group_id column with a foreign key setup to point to the groups’ table.

When I call $subject->group it returns null; it should return the Group model that the Subject belongs to. I can manually get the Group by calling Group::where(‘id’, ‘=’, $subject->group_id) and that works fine. The $subject variable is also working as expected.

What I’ve tried in the Subject model:

// Not all at once obviously, it's just easier to show what I've tried like this.
public function group(): BelongsTo {
     return $this->hasOne(Group::class, 'id', 'group_id');
     return $this->belongsTo(Group::class, 'id', 'group_id');
     return $this->belongsTo(Group::class);
}

web.php:

Route::get('/subjects/{subject}', [AppHttpControllersSubjectsController::class, 'subject'])->name('subject');

How I’m testing in my controller:

public function subject(Request $request, Subject $subject) 
{
    dd($subject->group);
}

dd($subject) returns a subject model object filled with expected data. Returning $subject->group() returns a group model object but no data in it.

What I’ve tried so far:

// php artisan tinker:
$s = Subject::first(); $g = Group::where('id', $s->group_id)->firstOrFail();

Returns

  IlluminateDatabaseEloquentModelNotFoundException  No query results for model [AppModelsGroup].

        $testSub = Subject::where('id', '=', 4074)->first();
        $testGroup = Group::where('id', '=', $testSub['group_id'])->first();
dd($testSub, $testGroup, $testSub->group);

Returns the subject and group model objects filled with the expected data. $testSub->group returns null.

I called

dd($student->is($testSub));

And it returns true

Something that does work is:

$subject->group()->get()

But that isn’t ideal.

Using ‘with’ either in the model as a protected member or calling the method, does not work.