Its a bug in CH. The question is if you can repeat it reliably and want to share with Adobe. There is a special report area for that, or you can mention @DanTull and he often sweeps in with a solution. If you don’t want help from Adobe, you can try holding down ALT and hitting the refresh button at the bottom of the scene window to flush caches and try and repair things. But then Adobe won’t be able to investigate and track it down.
Based on the error code, I think it is related to parameter disclosure/expansion in the properties panel for timeline selections. It corresponds to some UI data that is expected to be one type being a plain true/false value instead.
I did some digging in that code and haven't quite figured out how to get into the state where that is the case, though.
If I could get a zip of the repo.noindex folder for this project, I might be able to track down what got the data into that state. Since it is UI data and not project data, I think you can get the bogus data out by closing the project and then holding shift when you re-open it (that'll reset the data, which also means it will forget which scenes/puppets you had open and some other UI state details).