Tvheadend

I have compiled the driver for my Geniatech T230C DVB-T2 USB receiver and it seems to work.
But when I try to scan for channels with TVHeadend 4.0.8 on my Raspbian Jessie system TVHeadend reports:

:
2017-04-06 02:22:34.000 mpegts: 706MHz in DVB-T2 - scan no data, failed
2017-04-06 02:22:34.000 subscription: 01FC: "scan" unsubscribing
2017-04-06 02:22:44.000 mpegts: 546MHz in DVB-T2 - tuning on Silicon Labs Si2168 : DVB-T #0
2017-04-06 02:22:44.000 subscription: 01FE: "scan" subscribing to mux "546MHz", weight: 2, adapter: "Silicon Labs Si2168 : DVB-T #0", network: "DVB-T2", service: "Raw PID Subscription"
comet failure [e=this.el.dom is undefined]
2017-04-06 02:22:49.000 mpegts: 546MHz in DVB-T2 - scan no data, failed
2017-04-06 02:22:49.000 subscription: 01FE: "scan" unsubscribing
:

In the end it still finds only 3 SD channels but none of the about 20 HD channels of the German DVB-T2 broadcast.
I can exclude hardware issues since with http://www.dvbviewer.com/ I could receive all HD Channels in good quality on Windows 10.

What could be the problem?
How can I debug it? What should I test to get this working?