I've got an issue with making my Doom map

So while working on my 3rd map for an upcoming megawad, there is a visual bug. In-game, the stairs in one room and the floor in another look really glitchy. But in 3D mode in UDM, it looks fine. Any fixes?

Edit: I just realised that I've already made a post about this post. Sorry about that, I just have a weak signal from where I live and I can't see my other same post and also this one. So I cannot delete this post rn until it shows up in my profile.

try re-drawing the sectors. just trace over what's there and make sure each sector is really closed