I'm been doing a bunch of testing after replacing my Xeon E5-2696v2 + GPU and Supermicro motherboard setup with a Z590 + i5-11400 combo using Quicksync and have arrived at a stable solution that allows me to hardware transcode with the latest Plex builds.   I have issues with any Unraid release from 6.10.0-RC1 including RC2 and the latest test builds beyond that. Regardless of my setup including blacklisting i915 in favour of GPU Top I still have crashes when Plex uses hardware transco