Just to follow up this issue, same thing happening just now (Jul 16th 2020)...
I wasn't able to set UITableViewCell properly in IB and it gets me wrong frames, and margins, constraints, etc... Nothing is being rendering correctly even using the guide provided by the IB... Along with this issue, it doesn't matter which width do I use, it always throws a warning about to resize the cell from current to expected value and every time i go to the "Fix misplacement/update constraints" i get the same warning with new values. (lol).
However i decided to create collection view for everything (more work for layout), but now UICollectionViewCell is working right in IB :D.
Other approach i was doing before UICollectionvViews is to create UITableviewCell from code and attach to the content view a custom UIView Designed in IB and add constraints through code. (but i think this may confuse future developers so i migrated everything to collection view).