Ok, I will answer step by step:
I used PrusaSlicer 2.0.0, all default settings, 0.15mm OPTIMAL profile for the MK2.5S.
The bearing is not loose on the shaft, but doesn't need pressure to be seated (though I actually broke the shaft while trying to remove it). The bearing slide up to the flange easily.
Can you share me your PrusaSlicer config file (if you use it, even for MK3S, I have one), I will reprint the gears with your settings.