500 internal server error when editing specific poll in a post with votes (editing other polls works fine)

I just had a user create another post with a poll. Both the user and I as admin then voted (two separate votes, on two different choices). Then I as admin edited one of the polls choices. It worked just fine and the votes were preserved. I edited again and changed the other choice’s text, and it worked fine again.

For the other post it no longer works, but editing choices’ text worked just fine yesterday …

Any clues?