After updating to Anki 24.11, and re-optimising my parameters, some of my cards have had their intervals increased by an extremely large amount of time, for no apparent reason. For example, in the image below, you can see a card that before I rescheduled had an interval of 27 days. However, after updating to Anki 24.11 (and so FSRS 5), and rescheduling my cards, the interview changed to 6.67 years. I most definitely do not know this card, and a select few other cards that have had similar changes to their intervals.
Today I again tried reoptimising my parameters, but Anki said they appeared to be optimal - so, I rescheduled all my cards, and while that added about ~60 new cards to be due today (and before), those aforementioned cards still have an extremely long interval.
My FSRS parameters are 0.4203, 1.8758, 12.9786, 38.0504, 6.6361, 0.0159, 2.5039, 0.0022, 1.7216, 0.5497, 1.2369, 1.3874, 0.2428, 0.5271, 2.0570, 0.3068, 1.6111, 0.2612, 0.8798
, with a desired retention of 0.80. Let me know if you need any more information from me.