[-DDD-]

and the TBS6985 literally disappeared to the system, doesn't show with any modprobe command and not showing up in tvheadend under adapters, it's as if the driver just vanished (!?).

Just installing everything again from scratch and will provide a log with debugging enabled once done.

Do you see the TV Card in the BIOS? There were often BIOS Bugs with PCIe TV Cards in Series 7 and 8 Intel Boards,
maybe they are now in the Series 9 Boards also