To update, I had tried the steps above multiple times from the autosave and they always lead to the same results. Eventually I decided to not finish this quest now and do more exploring in the city. I picked locks and discovered places, gaining some XP each time. I went into the Scriveners Dormitory and picked a lock in there that spammed a 60 XP gained message so many times I gained about 10,000 XP within seconds. I was able to exit the house without a crash, but didn't want to save with all that extra XP. My autosave had been overwritten so I went back and reloaded my save in Purnisc's house, did everything from before and was able to finish the His Old Self quest without issue this time.