Gamecube over RGBs SCART losing sync on PVM-D20L5A

[Richtr8]

Hey everyone.

Recently I've been trying to use my L5 to play Melee on my PAL Gamecube over the same multi-out to SCART cable I use for my NTSC SNES. Gameplay is fine 99% of the time, but certain images cause the screen to flicker & sometimes even lose sync altogether. I've included a video to demonstrate just what I mean by 'lose sync'.

https://www.youtube.com/watch?v=zA1RpYCUOyI

Anyway, I'm not too sure what other relevant info there is other than that the 'cube is outputting 575i, & when it goes into the 'no sync' mode the PVM thinks the resolution has changed to a 16:9 one.