Nova MorphOne issue: 502 or 504 response on resource creation

I have an application which has an Address model which is used by many other models in a polymorphic relationship. A given model can have the trait HasAddresses which is shown here:

    public function addresses(): MorphMany
    {
        return $this->morphMany(Address::class, 'addressable');
    }

    public function primaryAddress(): MorphOne
    {
        return $this->morphOne(Address::class, 'addressable')->ofMany([], function (Builder $query) {
            $query->where('type', '=', AddressType::PRIMARY_ADDRESS->value);
        });
    }

So if a Model HasAddresses then they have an addresses relationship and a primaryAddress relationship.

The problem I am having is when I include the Primary Address relationship in my Nova resource as a MorphOne field that is required for creation. Either I get a 504 timeout error or a 502 error with no information. Nothing shows in the logs, and I have been unable to figure out the root cause.

The field DOES work if there is already a primary address and the user is updating it, but it does NOT work if the user is creating an address for the first time.

The Address model has an observer that runs some data manipulation to store things properly:

    public function creating(Address $address): void
    {
        //get the state by the name, or abort
        $stateId = State::where('code', Sql::EQUAL, $address->stateName)
            ->orWhere('name', Sql::EQUAL, $address->stateName)
            ->value('id')
            ?? throw new \Exception('The state provided did not match any known states in the system.');

        //get the county by the name, or abort
        $countyId = County::where('name', Sql::EQUAL, Str::replace(' County', '', $address->countyName))
            ->where('state_id', Sql::EQUAL, $stateId)
            ->value('id')
            ?? throw new \Exception('The county provided did not match any known counties in the system.');

        //get the city by the name, or abort
        $cityId = City::where('name', Sql::EQUAL, $address->cityName)
            ->where('state_id', Sql::EQUAL, $stateId)
            ->where('county_id', Sql::EQUAL, $countyId)
            ->value('id')
            ?? throw new \Exception('The city provided did not match any known cities in the system.');

        //get the zipCode by the name, or abort
        $zipCodeId = ZipCode::where('name', Sql::EQUAL, $address->zipCodeName)
            ->value('id')
            ?? throw new \Exception('The zip code provided did not match any known zip codes in the system.');


        $address->state_id = $stateId;
        $address->county_id = $countyId;
        $address->city_id = $cityId;
        $address->zip_code_id = $zipCodeId;
        $address->created_by = Auth::id();
        $address->created_at = now();
        $address->latitude = floatval($address->latitude);
        $address->longitude = floatval($address->longitude);

        // Remove appended (non-persisted) attributes from the attributes array.
        $attributes = $address->getAttributes();
        foreach (['search', 'countyName', 'cityName', 'zipCodeName', 'stateName'] as $attr) {
            unset($attributes[$attr]);
        }
        $address->setRawAttributes($attributes);
        return;
}

and that code is also used in the updating(Address $address) observer method.

Here is an example of a resource that does not work when creating a new instance:

class Trainer extends Resource
{
    use HasTabs;
    use IsRootResource;
    use NonReplicableResource;

    /**
     * The model the resource corresponds to.
     *
     * @var class-string<TrainerModel>
     */
    public static string $model = TrainerModel::class;

    /**
     * The single value that should be used to represent the resource when being displayed.
     *
     * @var string
     */
    public static $title = 'last_name';

    /**
     * The columns that should be searched.
     *
     * @var array
     */
    public static $search = [
        'first_name',
        'last_name',
    ];

    /**
     * The default property to sort on
     *
     * @var string
     */
    public static string $defaultSort = 'last_name';

    public function fields(NovaRequest $request): array
    {
        return [
            Text::make('First Name'),
            Text::make('Last Name'),
            BelongsTo::make('Type', 'type', TrainerType::class),
            MorphOne::make('Primary Contact', 'primaryContact', Contact::class),
        ];
    }
}

And finally, here is the Address model:

class Address extends Model
{
    use HasFactory;
    use HasTimestamps;
    use IsOwnedByUser;
    use LogsActivity;

    protected $table = 'system_addresses';

    /**
     * The fillable attributes
     *
     * @var array
     */
    protected $fillable = [
        ...Owners::FILLABLE,
        ...Timestamps::FILLABLE,
        ...Titles::FILLABLE,
        'uuid',
        'status',
        'addressable_type',
        'addressable_id',
        'is_primary',
        'address_line_1',
        'address_line_2',
        'cross_streets',
        'longitude',
        'latitude',
        'lat_1000_floor',
        'city_id',
        'county_id',
        'zip_code_id',
        'state_id',
    ];

    /**
     * The castable attributes and their cast types
     *
     * @var array
     */
    protected $casts = [
        ...Owners::CASTS,
        ...Timestamps::CASTS,
        'status' => AttributeStatus::class,
        'longitude' => 'float',
        'latitude' => 'float',
    ];

    /**
     * Retrieve an instance of the model factory
     *
     * @return Factory
     */
    public static function newFactory(): Factory
    {
        return new (AddressFactory::class);
    }

    public function getLongitude(): float
    {
        return floatval($this->longitude);
    }

    public function getLatitude(): float
    {
        return floatval($this->latitude);
    }

    public function parent(): mixed
    {
        return $this->addressable();
    }

    public function addressable(): MorphTo
    {
        return $this->morphTo();
    }

    public function isPrimary(): bool
    {
        return $this->is_primary == 1;
    }

    public function city(): BelongsTo
    {
        return $this->belongsTo(
            related: City::class,
            foreignKey: 'city_id',
            ownerKey: 'id'
        );
    }

    public function county(): BelongsTo
    {
        return $this->belongsTo(
            related: County::class,
            foreignKey: 'county_id',
            ownerKey: 'id'
        );
    }

    public function zipCode(): BelongsTo
    {
        return $this->belongsTo(
            related: ZipCode::class,
            foreignKey: 'zip_code_id',
            ownerKey: 'id'
        );
    }

    public function state(): BelongsTo
    {
        return $this->belongsTo(
            related: State::class,
            foreignKey: 'state_id',
            ownerKey: 'id'
        );
    }
}

I don't know why I am getting the 502 error or the 504 error. Any help would be greatly appreciated!

In a different / separate application, I have used this exact same approach with successful results. That version used Laravel 9.19 and Nova 4.0.0, and the current version uses Laravel 10.48 and Nova 4.35, which is the latest version I am able to use.