My usual routine is to update my Emacs packages on Sunday. After my last update, I restarted Emacs and Org wouldn’t load, complaining that org-assert-version was an invalid function. After a bit of messing around, I uninstalled Org-9.6 from my Elpa repository and deleted all the files. When I restarted Emacs, I got the builtin version of Org, Org-9.5.5, which worked perfectly.
The Org mailing list has a short thread on the problem but it’s hard to figure out what’s going on. Apparently org-assert-version is intended to deal with the repository being corrupted by files from different versions. There’s been a bit of pushback on org-assert-version and a patch intended to fix the invalid function problem by Bastien also received some pushback so it’s not clear when the issue will be resolved.
I’m pretty certain it’s not a mixed versions problem because I nuked my Org-9.6 repository, did a fresh install, and still got the error. I’m happy enough running 9.5.5 but I do wish this would get resolved.
In the mean time, if you see this problem, just uninstall 9.6 and let the builtin version take over. The Org maintainers are very good at getting things like this fixed so I’m confident that when I do my updates this coming Sunday, the situation will be resolved.