Anyone know anything ffmpeg? RA is crashing on hitting record

trying to spruce up my custom recording config file a bit, and it seems if i try to use libx265 the second i hit record it crashes if i use anything other than yuv4xx color which looks markedly worse than using rgb/bgr.

I can use libx264 but im trying to understand why its crashing with hevc.

is it broken, or is there some kind of limitation in place im unaware of?