Thanks for the responses, and apologies for the late ping-back - the semester has gotten away from me!
I'm almost certain that in the upgrade process I borked some directory permissions. In the end, I couldn't figure out anything useful, and it wasn't that hard to just wipe the installation and setup from scratch with 2.13. Which is what I ended up doing, and it's been working almost perfectly since. Posting a new thread to ask about a new problem I'm running into with Rserve, which was working, and is now not.