Fuck actions which are sufficiently quick seem to not consistently give rewards. In the 10-20k stat level (and >1k kink levels), I'm sometimes failing to get any progress from various fucks. My guess is this happens when they happen too quickly for the animation to show up? The same might happen for other actions, but if you repeat them the animation appears so it's not a problem. Obviously that doesn't work for actions you can't repeat.
That's a weird one, I think you're close with the fast animation and have a feeling this is due to the number's lerp being cut off early and not making up the diff. Not noticeable when you only lose 1 frame from a few seconds but very noticeable when it only runs for 2 or fewer frames. It's just a guess from some other issues Ive seen and hopefully should be fixed in the next update. It'll be something to add to the testing as least.