Similar problem here:
LibreElec (7.0.2) on Raspberry Pi 1 using the same hardware: CT2-4400. Austria, too.
TV adapter shows up in theadend's web-frontend, but even if I enable the listed "Silicon Labs S2168 : DVB-T #0", nothing happens.
Unfortunately, the 4.x documentation for tvheadend (configure_tvheadend) says "NOTE: TEXT REQUIRED" in almost all paragraphs that might be relevant to debug this :(
Any help/input appreciated.
Thanks in advance :D