This started happening recently; I believe after the update that caused many mods like Additional Camera Stuff and Random UI improvements to no longer be compatible with the game.
In a replay, and so far only in a replay, whenever I switch to any player, and decide to switch back to observer, the game's fps immediately starts dropping. In my case, it went from 90 to 20 at the start of a match!
Looking in the console, whenever this bug occurs, it starts printing this particular warning at break-neck speeds. Unchecking errors also made the game crash, which is why I'm actually able to provide a text file of the error, instead of a screenshot.
I'm unfortunately not knowledgeable enough in how faf works to understand the error, and from past experiences, documentation is non-existent. What the hell is going on in here? If needed, I can provide the entire log (Might have to trim it, as the above error gets looped for over 165000 lines.)