Sample clips so we can repeat the issue (or prove it's something local to your device) are useful. Pictures of artefacts aren't useful. I suspect it's something unusual about the media because stats show a stable and increasing number of C2 boards running the image and while I've deliberately tried to set people's expectations low since there are missing things and it's not perfect, I'm surprised (and pleased) at the overall lack of user issues being reported.
Well it seems my artifacts were an artifact. Cannot reproduce them anymore.
I restored the backup I made of Nexus so it is just as I left it last time. But now, no artifacts anywhere, not even the files I tried last time.
I can report that H264 1080p is working correctly for everything I tried. Seeking also works perfectly.
HEVC 1080p also plays correct but seeking in big blocks is 100% non functional. Fast forward works a bit. This makes resume is also non functional.
I did not try 4K media on a 4K source. 4k HEVC was a bit choppy on a 1080p monitor.
I use kodi mainly as a local network video player so I am gonna stick to Leia but i will keep an eye on the future releases/progress.
Nice to see so much is working now for the C2. Thanks!
Maybe chatGPT-4 can solve the HEVC seeking problem 
Then again, it might soon rewrite the entire video driver.