EDIT: Oops, ninja’ed by Graham!!! While I’ll leave this up anyway…
There were some issues with HLG playback reported in the v19 testing thread about two weeks ago - I guess they haven’t been fixed yet. If I recall correctly, there were actually two issues - on VP9 videos the TV would switch to HDR rather than HLG HDR; and on certain HEVC videos (but not all - something to do with the frame header) the Vero ends up signalling SDR rec.2020 instead of HLG.