MacOS: Delay between mouse click and movement but not on spellcasting

There's a noticeable <1s delay between when I click the mouse to move, and when the movement actually starts. This is not experienced when triggering spells with right-click, seemingly only on a request to move.

I understand my machine may be underpowered (Mac Air 2018) but the cpu/gpu meters are never pegged while playing the game.