3D Frame Packed (MVC) output with CoreELEC?

I have been trying to play 3D-MVC ISO/MKV as frame-packed 3D on my Dune-HD Homatics R 4K Plus box using Kodi 21.2 latest CE-NG and CE-NE, but playback always “stutters”, aka about every 1 second or so it jumps a bit. Played from NAS via Gbps, played from USB3 /storage directory, no difference. Tried passthrough, tried decode to PCM (jsut in case sync with audio could have made a difference). All the same. Info display does not show any CPU exhaustion, max core utilization below 40%.

How would i have to report this as a bug other then just writing this post here ? I already posted to the 3D thread, but no reply there.