ZDoom

I see, it depends heavily on available space to stand up. For default Doom player with height of 56 units and with crouch factor equals to 0.5 the mentioned issue happens in a sector with effective height from 29 to 32 inclusive.

https://drive.google.com/open?id=1zZkzr ... 8zMn_1OUvC

Here is a short test map, but I don't think this is map specific, but rather has something to do with the collision

Short video - https://streamable.com/nbcms

I cannot reproduce this. Do you have some modes loaded? In any case, post map and location in it where you noticed the issue.

I just noticed that if you crouch and go into a small vent or something using toggle crouch button, then you try to stand up by pressing it again - nothing happens as expected, if you go out of vent the player will automatically stand up.
however, if when you are vent you press toggle crouch to get up, and then press it again, and go out of the vent, toggle crouch does not make you go to standing position, you have to use jump button to toggle the state.