In MCPE, when you play on D-Pad, you can move slightly on the right/left when you shift your finger from the move forward button to the left/right (basically WA, or WD in pc) and for some reason, it does not work sometimes and MInecraft thinks that you are interacting with the world and not touching the button. 

(This was a bug from 1.17 and has been fixed but the new update brought it back even worse)