I've been having this same (or similar) problem for a long time, without realizing it. Tvheadend will not show all available services. I thought it was bad reception (I'm using an antenna, not cable). But then I recently tried MythTV instead, and it received all stations perfectly. I went back to Tvheadend, and again, it did not show all channels. Out of the 52 channels MythTV receives, Tvheadend can only see 35. However, it does actually see about 52 services, but in the list many are blank, like it could not receive the information from them, and I cannot use them. On occasion, an odd symptom will occur. The name(s) of one or more services will be swapped with the name of a service that tvheadend cannot receive. It is usually temporary, and doesn't affect channel reception (I don't suddenly receive the missing channel). Also, I'm not on DVB-C. I'm in the United States, working with ATSC digital channels. Not sure if this means it's a different problem. This has been with every version of tvheadend I've tried (2.12, 2.99, 3.2, and 3.4).
Is there a way to have MythTV find the channels, then import the information into tvheadend and just turn off service scanning completely?
Sadly, I'm back to using MythTV until this gets resolved. Neither works perfectly, and I wish there was a Linux TV server with the best features of both. Tvheadend changes channels more quickly, is easier to set up, has a MUCH nicer web interface, streams channels more smoothly across my LAN, and I can easily copy/paste icon URL's from the TV station's web site (MythTV's channel icon search is terrible, gives badly outdated icons, and doesn't let custom icons come through on XBMC). But MythTV can timeshift, receive EIT information (tvheadend apparently won't work with ATSC EIT), and is better and faster at service searches. Once tvheadend has all these things, it'll be just about perfect. I know you guys are working on it. It's just hard to wait when there's so much TV to watch!