Hello! Thank you for your helpful input!
It seems that the real issue was a combination of the problems you listed. While I wasn’t able to pinpoint a single error, I believe I had a subdeck with alternative settings, I was already learning cards, and I was using a filtered deck.
I have since corrected the problem by making sure all the setting of all subdecks are under my default settings and then enabling FSRS.
Thanks again for your help!