Probably how the scaling is off while you drag windows from/to hidpi displays. The scaling is only adjusted once the pointer moves to the other display.
At least that's how it was for me when I used a high dpi display (160 dpi) 2 yrs ago. (I switched back to 90dpi at some point, so they might have improved it by now)
That only applies for non-integer scales. If you run at clean 2x or 3x everything is drawn at native scale, unless the app doesn’t support HiDPI in which case it’s drawn at 1x and scaled up.
At least that's how it was for me when I used a high dpi display (160 dpi) 2 yrs ago. (I switched back to 90dpi at some point, so they might have improved it by now)