I just updated to InDesign 2021. Now when I open a previous file, some text boxes appear blank.

I just updated to InDesign 2021. Now when I open a previous file, some of the text boxes appear blank. Some appear as they should. The ones that appear blank do not all share the same paragraph style, so I don't think that's the issue. I've checked for items that might have wrap text selected and can't find any. I'm not sure how to fix it. When I try to create a new text box,  it won't let me type anything it. Help!