If you create a brand new layout in your file from scratch (don't copy and paste from the problem layout), does it show the same behavior? If it works and the original layout does not, perhaps the layout is damaged.
If you recover a copy of your file, does the recovered copy work correctly? The file, or an index or two may be damaged. You can try rebuilding the file's indexes by saving a clone of the file and importing all your data into the clone to see if that helps.
Best practice is to not use a recovered file, but instead replace it with an undamaged backup copy of you have one.
So you are assuming that the file is damaged. What leads you to that?
I have rebuilt the layout from the ground up and the problem went away. However, as I did that I removed all use of the "Self" function from conditional formatting, adjusted all conditional formatting to always include a text color (black) and adjusted the privilege sets to allow for modifying layouts. I also once again adjusted the portal to make sure all fields are on the portal correctly. What was the likely issue? Don't have a clue but the problem went away.
I have now found the same problem on a similar screen and am attempting to adjust said screens conditional formatting so that it matches the first screen. If this does not work I will buy into the idea of a damaged file (or at least a damaged portal or layout) and once again rebuild the screen.
I wasn't assuming that it was damaged, just suggesting a simple test to rule out that possibility.
I'd certainly examine the conditional formatting issues before concluding the file or layout was damaged.
I'd remove all conditional formatting from the problem layout and see if that fixes the problem. If it does, I'd add one conditional format expression at a time, testing after each until I either have everything working or have replicated the problem.