Did a ton of work with actions lately and ran into around 4 cases of weirdness in PS CC 2017.
One bug I forgot, but this one I tested and is also in 2020.
When a layer is inside a folder and you move its mask to the folder instead, the mask is moved. If you play the recorded action, the mask is moved *and* leaves the original. (This can lead to actions breaking and I have to solve it with a script to make sure.)
- - -
2 other things I got which may be due to a damaged file...
(1) one action was impossible to record as a called sub action (I made a new one and moved its steps into it, which solved it)
(2) still, that same action -- when called after a Stop at the end of a huge action -- played alright but the selection didn't move to the next step. So when pressing 'Continue' it executes that action again (and again). I'll try re-recording the whole action for this one.
I wish I remembered the fourth and more important one...