[VU+ Uno4K] The receiver fails to tune into a channel while watching via HDMI, but successfully streams to Plex/Kodi

[bk109]

Long story short, I noticed that the Uno4K box I've been using (mostly) problem free as a DVB-C DVR/Retransmitter (mostly via Plex) fails to tune into certain channels(which worked fine in the past couple of weeks) when outputting the signal via HDMI. Initially I assumed that it's a signal/CAM issue, but then I noticed that I could still stream those through Plex or Kodi or when using the TV's built-in tuner. As I don't have any idea whatsoever what to look for in the debug log of an enigma2 box, can someone please tell me if it's a local issue (and if so, how to resolve it) or if the root cause lies with the cable operator (in which case I'm SOL) ?
Edit: To rule out a software bug in the latest OpenVix packages, in addition to a signal rescan, a factory reset and a reflash, I also tried OpenPLI, VTI 14.0 and the latest official image from Vu+ to no avail.