Not the same thing but when changing speeds i saw those changes in the past.
I think they show set speed and some kind of real/measured speed when there is a diffrence.
You could try 5% lower speed to check if its gone (rpm could be near where it will show 10% more or less) or if maybe your fan has some problems moving dirt/malfunction then check for that.
I’ve actually noticed the following. When I print with the door closed, the auxiliary fan starts to fluctuate between 70% and 80% after an indeterminate amount of time. When the door is open, this behavior no longer occurs.
The P1S doesn’t have a door sensor or anything similar, does it?