Yes, the problem of not finding DVB-T2 (HD) channels during a scan is specific to the Plex Tuner Service.
The issue of blank picture/no sound is specific to using tvheadend/tvhproxy and NOT native tuners in Plex, and can be worked around via the fix I posted earlier in the thread.
I can provide any logs you want but note the Plex Tuner Service does NOT find the HD channels with my card, which is an TBS 6985 Quad DVB-T2 tuner card. This is why I have to use tvheadend.
Yes I have tried full scans and also logged into the Plex docker, and configured the correct frequency, QAM etc in the .ini file for the DVB-T2 Mux but still it fails to find the HD channels. As per my earlier post I believe this is an issue with a PLP setting that Plex needs to do.