[I already resolved this but I thought I’d share for future users that may run into it.]
I attempted to load a Kite Demo asset, which froze the editor. One I thought I was already using. (It’s probably best to let it take all night if it needs to.) When I attempted to reload the project it would just crash. There didn’t appear to be any useful info in the log. So I unset the default map, which then allowed it to load. But then opening any blueprint would crash.
Now there was a critical error in the log followed by other errors:
It turned out that a Paragon character in my project had corrupted somehow. I believe a physics asset due to the error message. I had started working on physics for that character that night. So I resolved it by removing the character’s folder from the project. Wasn’t able to determine which asset or in what way, so I removed the whole thing. Then everything is working again. (Time to backup more.)
Also I did try copying the project to 4.22 as I was told a bug was fixed in that version. That gave me some errors, but ended up copying, and blueprints opened at that point. However in my case a plugin I rely on doesn’t work with that version.
Hope this is useful if someone else runs into anything similar!