Tvheadend scan no data, failed with Geniatech T230C

I bought a Geniatech T230C and installed LibreELEC 8.0.1 and the addon Tvheadend 4.2.

When I scan for (DVB-T2) channels in the Berlin area I only obtain

"scan no data, failed".

Only these 3 SD channels at 682 MHz (channel 47) are found:

service-mapper: DVB-T Network/682MHz/Channel 21/Euronews: success
service-mapper: DVB-T Network/682MHz/1-2-3.tv: success
service-mapper: DVB-T Network/682MHz/JuweloSK: success

I have tried different pre-defined muxes and even left this field empty but nothing helps.

How can the other channels be found?

I am not sure at all, because I don't know what I have to enter.
I just chose Germany-Berlin and after this failed I chose Germany-Brandenburg, default and finally left the field empty because I was told that would scan all frequencies.
I would be glad about information what to enter that the channels should be found.

But how?
Are there any instructions about this?

But what are the settings?

Thank you, now it works!
When I edited the channels I found that they were set to DVB-T instead of DVB-T2. Maybe this was the problem.
Anyway I found 19 channels.

But now every channels appears to freeze every second and the audio gets out of sync. Then after some 30 seconds kodi starts to buffer again. Sometimes the audio disappears completely and doesn't come back and also playback stopped completely a few times. The temperature gets very high also I have opened the case and use heat sinks. It seems as if the RPi 3 is not fast enough for the h.265 decoding.
Does anybody not have this problem?