On clean installation no scan issue. As I mentioned earlier I installed WebGrab++ to be able grab EPG from internet and try to fix using channel config with mixed dvb-s/dvb-t/dvb-c in tvheadend. After successfully running WebGrab++ I disabled all other sources for EPG:
1. in DVB Inputs -> TV Adapters: 'Over-the-Air EPG'
2. in Channel/EPG -> EPG Grabber Modules: allowed only 'Internal XMLTV'
After this EPG config I got as side-effect 'no scan data' for any attempt to scan any network service.
After reverting config in Channel/EPG -> EPG Grabber Modules I found: Disabling 'EIT: DVB Grabber' is disabled scanning for internal tuner.
Probably it is a hint for fixing internal dvb tuner scanning issue.