Updating Premiere CC is not without its problems. Here are some solutions that appear to work in most cases to fix the terrible bugs that happen when updating from one Premiere Pro to the newer one.
-Keep working in the older version if necessary by right clicking and saying "open in Premiere 2024" for example
-Open the newer version of Premiere Pro CC on it's own and create a new project then import the bugged project into that and save it as the current date
-Clear the media cache if all else is failing
Sometimes one of more of these items will work if not one alone - you need to keep working to outsmart the issues CC is facing! Keep the faith!