snapshot.debian.org was a great help! Though I had trouble with apt to deal with the downgrade with depedencies, aptitude's interactive UI helped a lot.
As for the xpra issue, it seemed to be something about xpra itself. I just found xpra was somehow not in the repo anymore.
https://tracker.debian.org/pkg/xpra confirmed the removal of xpra, and tracking that showed that there seemed to be some issue with moving xpra from sid to testing.