I have a raspberry pi installed with debian 10 operating system. When I tried using the GUI login, it was asking for username and password again and again in loops.
The password was correct and there was not error messages on the screen. I even tried changing my password to a new one without any special characters to check whether it was related to the locale of my keyboard. But it did not help.
Finally I solved the problem by installing the following package and rebooting the Pi.
sudo apt-get install lxsession
Hope this helps someone. 🙂