Admin Login reloads/redirects to same page

Hi there,
I’m new to Grav and I’m working my first One Pager. Now, without having changed anything, i’m experiencing a strange behaviour - when I put in the right credentials in the /admin Login Form (I’ve tested by resetting the password a few times) the page reloads without any notification or error on the debugger.

  • I’ve cleared and disabled caching
  • I’ve reset the .htaccess file
  • I’ve reset the system.yaml file
  • I’ve tried to access the /admin/config/sites directly, but it still shows the login form
  • I deleted the [user].yaml to create a new user, but the form shows an error “Oops there was a problem, please check your input and submit the form again.” for no particular reason (another issue here)

I’m using the landio theme running on LAMP.

Does anyone have an idea what else I could try without reinstalling grav again?