Everything seems fine. You could try to change your HDMI cable and/or whitelist resolutions to see if it solves the issue. If not, forcing 8-bit seems to be the only way to make this working. I’ve Pioneer VSX-933 and don’t have this problem.
I suspect you know that both your Kodi box and your AVR doesn’t support HDR10, so if you wan’t to watch 10-bit HDR content, you have to swap both or connect your (new) box directly to your TV as your AVR can’t passthrough BT.2020.