I'm encountering the same issue with what has been described in the post below:

https://wpforo.com/community/faq/login-problem-menu-is-not-changed-and-weird-logged-in-behaviour/#post-38918

I've since then tried:

1. Installing http to https plugin (Really Simple SSL)

2. Cleared cache. I am not using any external cache plugin

3. Hard flush permalink (wpForo)

4. cleared cache (wpForo)

But the issue seems to persist. I tried logging in with a non-admin user, nothing happened, the login doesnt turn into logout and I still cant post anything, as if I've not logged in at all. I first notice this issue when trying to perform a test registration, I've disable email double opt in due to it doesn't work. But despite registered without double opt in, nothing happended. It doesn't redirect me or whatsoever.

Here is my website: https://partnershipmarketers.com/

I've also enabled debugging mode, in case wpForo team wants to debug it.