Sometimes you can't pass under them, and sometimes when you can pass under them, you get stuck, and you are unable to get move or do anything.

I didn't start recording as soon as it happened. It's at Tisy, and from the footage you probably can gather more information about the location. It may seem like I'm stuck because of the zeds, but that's not correct. When I got stuck I was in a prone position and I couldn't go forward or backwards, zeds noticed me and started punching me. Then my character somehow stood up but I was still stuck.

I wanted to go under one of the concrete walls that are usually surrounding military bases, and some of them have gaps under them, quite a lot of time I struggle to get under, and on even rarer chance when I do get under, I get stuck and unable to move. In this situation zombies started hitting me, but after waking up from uncon, I was free to move again (and deal with the zombies).

I guess the easiest fix would be to increase the hitbox gap to make sure that players don't get stuck, or something like that.
(Game version: 1.12 exp, but I've had it happen on other versions too...)

These type of walls, but the variant with the gap under it.