Run composer update command and check if it solves

Thanks for the suggestion, bsfsos, but I ran composer update and even tried self-update. The problem remains. I don't get understand, the files are clearly there and read/write access is ok.

Does the $namespace variable in RouteServiceProvider.php match the namespace of Auth\AuthController?

Wel, tkprocat, my I found that the RouteServiceProvider $namespace variable is set to null. There was a commented line setting it to 'App\Http\Controllers'. I tried changing it back and running a composer dump-autoload, but then none of my pages work and I get errors like "Class App\Http\Controllers\SiteController does not exist"

I think we may be on the right track, but I am still lost and in need of a solution.