The "recently opened files" comes from one of the files in the preferences & other folders that is intentionally not removed during upgrades, or you would lose all your other things like keyboard shortcuts & such.
As to an improper installation of one version, that can happen. I've had times where I needed to uninstall with the Adobe CC Cleaner tool ... after renaming several of the layouts & preferences folders so PrPro wouldn't see them but I could still get my old keyboard shortcuts setup & such from them after a new install.
That Adobe CC Cleaner tool does get nearly everything the programs put on disc, and after running it, a reboot and reinstall takes care of most install issues. There's a couple things to know past this but I won't go into everything right now.
Neil
I solved my problem 75%. It turns out my Windows profile is corrupted and everytime I uninstall Premiere (using Adobe Clean Tool) and re-install, Warp Stabilizer is missing and Premiere is unstable.
Technical support had me to uninstall via the cleaner again, create a new Windows (administrator) profile, and reinstall Premiere on this profile. Sure enough, everything returned to normal.
I say this fix my problem 75%, because I have to log into a another profile on my machine and I don't know the true cause (or fix) for my main profile, but this is better than nothing. I hate to reinstall everything and get my preferences just the way I like them.