Steps to reproduce the issue

• Set up a login menu item that is a different component from the home menu item.
• Using the Edge browser, use an extension to add sec-gpc: 1 to headers.
• Try logging in.

Expected result

You log in normally.

Actual result

You get the error:

0 - Invalid controller: name='user', format=''

System information (as much as possible)

Server:

• Joomla 3.10
• LAMP Stack
• PHP 8.1.12
• MariaDB 10.6.8

Browser

• Windows 10 with Edge installed.
• The user originally encountered the issue with the "Avast Online Security & Privacy" extension installed, but just the header is enough to cause the issue for me.

Additional comments

The issue seems to be that when the form is submitted, the home page menu item controller is used instead of the login menu item controller. That causes issues in getInstance() in BaseController.php, generating a non-existent file path and throwing that error.

I'm not sure whether you'll look at bugs for Joomla 3.10, but it might be worth looking into whether the problem exists for Joomla 4 too.