After more testing it's just getting worse. every crypt door or anything like it just makes the ground go crazy (they are basically portals themselves), then I use the portal and it goes back to OK. can't build on shifting terrain so I'll probably have to abandon this base. there's about 6 hours I'll never get back.

Originally posted by L1m3r:

Looks to me like sth. is borked. No way should/could one hit with the pickaxe "remodel" so much ground.
-> I suspect the world save to be corrupted.

See if the mod upgrade_world[github.com] can help. Do NOT forget to make a backup!

I used mods in the past, not for me. I was actually hoping I could fix it with dev commands