I tried to turn off all the plug-ins, switch to the default theme with no components and still the same. Did not try restarting in between. Or is it important to remove the components fully from the .yml file, not just disabling them?
Yes, removing them from the configuration file is preferable. In rare cases, a disabled plugin can still have an effect on the forum (there are documented cases, but I don’t have the links), and completely uninstalling it can solve issues.
Basically using admin side to disable a plugin works only when it affects on user’side. It doesn’t touch server side. But I’ll stay corrected if I’m wrong.