So I uninstalled CF Update 12 (because of the error I was hitting related to GENERATEDKEY), and while that worked on one server, on another it appears to have hosed ColdFusion. Any suggestions to resolve? (other than a full reinstall of CF?)

My Update 12 did not uninstall properly either and left the server in a broken state. Replacing the directory with a backup did not help either so we had to restore from a snapshot. I'm assuming some registry change or something else outside the CF directory broke the install.

We ended up doing a uninstall/reinstall.

Did you do the uninstall through the admin UI? I did, and it worked fine. Asking because I mostly do patch upgrades on the cmd line, it's been much more reliable than the UI. My recently trashed CF instance happened when I saw how smoothly and easily that rollback went, made me overconfident that updating from U2 (not 12!) to U11 in the UI would work. Very much no, for me, but it's possible that there was already rot at the core from previous attempts, even though the server appeared to be stable. I'm swearing off the admin UI, at least for now. And reinstalling 2021 from scratch, having uninstalled it completely due to borkedness.

Yes, uninstall via the UI. cc @Marc Funaro

Did the uninstall hang? Throw? Appear to complete correctly, but the server was fubar after? Asking because the main failure mode I've seen installing updates through the UI is it just hangs forever, and when you stop it manually it's left a mess.

I think it appeared to complete but the server was fubar after.