FSRS Optimization Gives Unstable Results

I have a French deck that I've been creating and reviewing daily since June. I've been using FSRS the entire time. I've made about 2000 cards and have 700 still new.

I have installed the FSRS helper. I've reoptimized the parameters a few times. And I've used FSRS helper to reschedule after optimization. What I've noticed is that the difficultly calculations and number of upcoming reviews seem to fluctuate a ton. Is this expected behavior?

(I know there's no need to re-run optimization frequently. I noticed that the FSRS scheduling seemed to change a lot after an optimization, so I ran it a couple times over a week to see if it stayed consistent. And it didn't.)

For example:

Before reoptimization on Aug. 9, my deck was calculated to have an median difficulty of 4%. Today, on Aug. 12, before reoptimization, the median difficulty was 15%. Afterwards, it is now 10%.

Before reoptimization today, Anki wanted me to do 44 reviews tomorrow, and 29 reviews each day on average for the next month. After reoptimization, I have 13 reviews tomorrow, and 21 reviews each day on average for the next month. (And before optimization on Aug. 9, it was back at 21 reviews each day on average for the next month.)

So, the optimization feel kind of unstable. Is this just an artifact of inexact math simulating human learning?