Web Interface fast logoff after ~2s

[PickleSalad]

Expected Behaviour:

If I log into the web interface via the login page http://192.168.0.144/admin/index.php?login and enter the right credentials, I stay logged in until closing or terminating the session.

Actual Behaviour:

If I log in to the web interface of my pi using ctrl+enter, I get into the settings menu but it takes about two seconds before I am greeted with the login screen again after the next click. If I only use enter, I stay on the login page as if I pressed F5. This occurs on the PC that is connected via lan to the router, which in turn is lan-connected to the pi. When logging into the pihole interface on my phone, this does not happen. The pi does not have WiFi enabled.

Somebody seemed to have the exact same problem here, but the his problem seemed to be missing/wrong permissions on /etc/pihole/pihole-FTL.db while mine is

$ ls -l /etc/pihole/pihole-FTL.db
-rw-rw-r-- 1 pihole pihole 53248 Oct 7 12:01 pihole-FTL.db

so I think this problem is different. Does anyone have any ideas what the problem could be and how to fix it?

Debug Token:

https://tricorder.pi-hole.net/D6uipjqU/

[PromoFaux]

Do you have something that disables cookies? The web interface uses a cookie to know that you are logged in...

[DL6ER]

Can you run

df -h

to check if your disks are full? If so, Pi-hole may not be able to store your session. Other parts of Pi-hole have been carefully engineered to not be affected (too much) by no storage available.

[PickleSalad]

(@)PromoFaux I think you're on the right track. In Firefox's private browsing, I can access the page. Thank you for the hint, I will have a look at the settings and extensions, that should solve it. Thank you!

(@)DL6ER Thank you for the hint, but in my case this does not seem to be the issue.

Edit: So nothing blocked the cookies but everthing worked again after deleting the cookies once so I suspect that there was a faulty cookie set or something...?