Well after about a month, this issue seems to have resolved itself. I tried to fix this and test within PIE nearly everyday over the past few weeks, and it only started properly working again this week. I truly don’t know what the original cause was, or how it went away. I did at some point rebuild the source engine, but that was a couple weeks ago and it had no effect when I originally tested afterward.
Edit - In case anyone manages to find this post, this is what fixed all my issues: