I can answer this!
I had the same issue with DVB-T2 muxes not being scanned correctly (albeit in Belgium).
Using this guide : Bug in Scanning DVB-T2 with QAM256 in UK - #6 by Biskyt
and editing the .ini file as shown, I was able to force Plex to scan the mux containing the HD channels (again, in Belgium).
Try it out and let me know!
