+1 to this.
Some more notes that might help debug:
Switching to a wired Sidecar connection (harder than it sounds - disable bluetooth/wifi on both devices to ensure it's USB) helped with some of the display corruption.
However, I now see a weird issue where when a channel has been playing for a while, ending the track (either by hitting Cue to return to beginning, pausing it, or fading it to zero) causes Sidecar to freeze and need a reset by plugging/unplugging. If I try to reproduce by loading a track and immediately fading it out or resetting it, it doesn't happen. Sometimes the track will end then when I turn the track selector on my DDJ-400 it freezes then. Not sure if this is correlated to the controller event or to the screen refreshing.
This does not happen to my Sidecar connection when using other apps (including ones that often update the screen like watching YouTube videos, even in full-screen mode), seems limited to Rekordbox both in windowed or full-screen mode. The whole Sidecar connection freezes (mouse pointer won't move etc) so it's not just RB that's freezing. But it does seem limited to happening when I am using RB on the Sidecar screen.
I have limited space on my DJ table so using the iPad as a second screen via Sidecar would be nice!