You are the real MVP. Thanks!
It happens when i activate the plugins in a specific order. Here’s a video of it https://youtu.be/5sA63Osn5OA
And as i said: more plugins i have, more severe is the malfunction
Only the plugin. The theme is the standard Twenty Twenty-One Version: 1.3.
To reproduce the problem I installed a clean wordpress 5.7.1. Then Elementor, bbPress and the test plugin. Then I activated them in the same order. At the moment that I activate the test plugin bbPress menu items literally disappear.
PS: in this configuration I am able access the forum as a user. But when i discovered it on my working site the first time, forum pages were blocked as i described before.
I haven’t noticed any issues with other plugins at this point.