I think a lot of that's due to a few rendering methods available on Unreal that developers often end up turning to.

I can't remember if it was texture streaming or level streaming that's occasionally been a very noticeable visual blight. I think volumetric fog was another one that can be rather obvious and sometimes irksome.

One thing I used to remember sometimes being annoying in Unity was tone mapping, but that may have been more specific to a certain set of games I was playing some years ago.