I got this from a two week old posting. I was looking for an answer to this very same problem!
“On some tablet, after working on a mesh for some time, if you zoom in (alt+click+drag on the canvas) and it hits the zoom limit and starts zooming in on the canvas, sometimes when you brush (even the tweak brush) it will edit only one poly point at a time, like when you have your brush to set to the smallest size and brush at that size. Regardless how big you set the brush. If you zoom out to actual canvas size, it works normally, but it does that again if you zoom in too close again.”
Please someone help! This problem is maddening! I’m squinting to see what I’m doing because zooming in to much makes editing the model impossible!
Thanks in advance!