I am hesitant to say that I have good news or that I have fixed anything...
I honestly don't know if there is anyone left still using this site after all the problems we've had.
That said, I noticed that there were some very recent (as in yesterday/today) commits to the development branch of kbin that look like they address the issues that fedia has been experiencing. I moved fedia to the development branch and reloaded some things, and so far, no error 500's.
But, caveat emptor, we are on the development branch of early-in-its-lifecycle open source software.