Upgrade from RH10 to RH11 - cpd, failure to Close, failure to Import PDF Comments

Hello, am looking for help with a recent conversion of a project that has been upgraded from RH8-9-10 and now trying to go into 11. Apparently when going from 10 to 11, the author had similar issues to what I am having now and had to rebuild the entire project using existing files off the published version. Issues are: cpd error message; project won't Close Project, Close, or Exit (requires Task Manager); and it will not Import Comments from PDF. On our first attempt to upgrade, we experienced more and more lost topics (had an X on them in the TOC) and finally all files were like that. Reverted to 10 at that point. Have tried removing cpd / xpj / double-clicking the hhp (?) and a few other things. Any help appreciated! Thank you.