Since you are able to replicate this I suggest you record the sequence of steps using the Problem Capture system (from within the SWX Rx). DEFINITELY get your VAR involved. If they can replicate it and do not have a solution then they will send it off to SWX and you will get an SPR. At least then the good folks in Waltham will get their hands on it and can look into it and fix it for you and everyone else.
Can you move the drawing file to another folder so SW says, "Huh?" when open the drawing from the part/assy and then create a new drawing.
You don't have totally populate back to where it was, but at least put the DT in and see if it continues with a new file.
If there's joy, then recreate the remainder of the drawing's content.
As Dennis said, contact your VAR, which is why I said "move", not delete. Other people still may want to peek inside the drawing file even if a new file behaves.
Looks like you might be a lone ranger bud. Inserting the file into a new drawing and placing a new table exhibits the same behavior. I beleive it is somehow contained within the excel link or some error related to text.
Deleting the table and creating a new one with the same information resolves the problem.
I had an issue with entering text into an annotation which started displaying the background coding that was suppose to be controlling the font. Might be unique to 2018.