HEVC 10-bit colour change

[NathanBluebook]

I've been experimenting with HEVC / H.265 recently and I've been seeing an issue with my 10-bit encodes. In certain frames there's some minor changes in colour compared to the source material. 8-bit encodes with the exact same settings don't have this issue. And I also see it in both grainy and clean sources.

Here's an example [click on image or use left/right arrow keys to move between the two frames]: https://slow.pics/c/HSrvtDBt (look at the light hitting the back of his head and the yellow bead on his necklace)

Does anyone know what might be causing this please?

Here's the HEVC parameters I use:
ctu=64 / max-tu-size=32 / tu-intra-depth=1 / tu-inter-depth=1 / rdpenalty=0 / me=3 / subme=3 / merange=57 / no-b-intra / no-amp / ref=5 / no-weightb / lookahead-slices=4 / min-keyint=23 / bframes=8 / aq-mode=3 / aq-strength=1.0 / rd=4 / psy-rd=2.00 / psy-rdoq=1.00 / rdoq-level=2 / no-sao / no-open-gop / rc-lookahead=25 / scenecut=40 / max-merge=3 / qcomp=0.6 / strong-intra-smoothing / limit-refs=3 / deblock=-3,-3 / qg-size=32 / pbratio=1.30

[benwaggoner]

How are you playing it back? Some players do different things with 10-bit and 8-bit source when viewing on an 8-bit display that could cause some differences. That would be the first place I'd look. Like try playing back off USB in a HDR-capable TV that will have a 10-bit pipeline.