Don’t Reposition cards in play
Don’t reposition cards on board while spells/triggers are on the stack.
Eg I had one plumecreed escort in play, and a mockingbird copy of an opponent’s creature. They cast a removal spell targeting my mockingbird, I cast another plumecreed escort to give the mockingbird hexproof. I click on the mockingbird - or where it just was on board, but it’s location on the board was changed when the escort resolved so I just gave the new escort hexproof on itself.
I never think about how arena will auto-group & reposition similar cards and it’s not gameplay space I should have to keep track of or anticipate on top of everything else in the game. Please do not change the position of any cards in play until everything on the stack has resolved.
Or give us the option to auto-group/reposition cards & agree to the new positioning.