Plex (Docker) HDR Tone Mapping not working anymore (hw)

Plex Media Server NAS & Devices
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Server Version#:1.23.1.4571
Player Version#: 1.31.1.2262-74fdc6b7
PMS version: 1.23.1.4571 (plexpass) within Docker (Linuxserver)
System: Synology 920+ (DSM 6)

I moved quiet a while ago to Docker Plex (Linuxserver) to enable HDR Tone Mapping (hw transcoded) on my sinology NAS (DS920+).

I just recently noticed (I can’t state exactly from which version) that tone mapping (hw) stopped working, meaning when I transcode (4K->1080p) with tone mapping enabled the CPU usage goes up to >80%.

When I switch of tone mapping, transcoding (hw) works still fine in my Docker/Plex.

Is this rather a Plex problem or more likely a problem of the Linuxserver/Docker build?

Thanks!