When are HOOKS in Filament really called?

In reaction to the Error, I have described in "How can I prevent an Exception if the Select-Options in a relationship has a NULL value?" I tried to use Hooks to fill missing values in 'working_name' as:

protected function beforeFill(): void
{
    // Runs before the form fields are populated from the database.

    $toBeUpdatedOnes = Project::whereNull('working_name')->get();
    \Log::info('EDIT beforeFill found records ', $toBeUpdatedOnes); // Log the incoming data

    foreach ($toBeUpdatedOnes as $toBeUpdated) {
        \Log::info('beforeFill found record ', [$toBeUpdated]); // Log the incoming data
        $text = 'missing working name';
        if ($toBeUpdated->description == null) {
            $text = $text . ', ID: ' . str($toBeUpdated->id);
        } else {
            $text = $toBeUpdated->description;
            if (strlen($text) > 120) {
                $text = substr($text, 0, 120);
            }
        }
        $toBeUpdated->update(['working_name' => $text]);
        \Log::info('beforeFill updated record ', [$toBeUpdated]); // Log the corrected data
    }
}

I have seen the LOG-Entry once, but only once. The other times I got the above mentioned Error. That means for me, the OPTIONS-List is created before the FILL. I even tried it with mount() but with the same (Error-) Result. So I am not sure, whether and when the HOOKS are called.