If you shrink the player character or have any small humanoids in general, they start to control as if they were walking on ice. I expect them to continue to control as normal regardless of size. The issue happens consistently in all situations as far as I can tell.
I remember this bug started happening after the humanoid physics were tweaked a few months ago. There was a “heads-up” post about it somewhere but I’m unable to find it.
Small Humanoids (BodyScale 0.5 and lower) have an “ice skating” effect when moving around. It takes a long time for them to accelerate / decelerate. This issue may have regressed if it was previously fixed.
I have created a simple open source repro place here to see the issue clearly. Default humanoid size is set to 0.2.