LUCI is inaccessible, was slow before

Hi there, my Turris Omnia runs Turris OS 5.2.0 and I cannot access LUCI anymore.
It was slow on 5.1 for some reason and now with 5.2 it is inaccessible.
The login-page creates 100% load for ~5 seconds and then drops me back to the login, no errors at all in logread -f.
foris and reForis work fine.

Got it to work via https but now every request takes ~5sec or more, which means most pages take >10 seconds to load.