Bug? 4-finger swipes cause 2-finger swipes (scrolls) at same time

I have successfully linked 4-finger swipes to various triggers (specifically App Switcher, Cmd+tab key combo). 4-finger swipes are always recognized fine. However, at least half the time they are simultaneously seen by the system as 2-finger swipes, causing scrolls at the same time as the BTT action. This makes it hard to use really. Is this a bug and/or can anything be done about it?

On a lark I tried ticking the option buried in settings → trackpad → swipes to prevent 4-finger swipes from causing 3-finger swipes at the same time. Didn't help. I also tried changing 4-finger swipe sensitivty = 2-finger swipe sensitivity. Also didn't help. (I have not yet tried ticking "aggressive mode", whatever that is.)