More common than assumed since most do not peruse those channels.
My strategy? Try to tune them all in manually if possible. If that doesn't fix it, perform a factory reset of all equipment involved and start from scratch, preferably, using manual tuning again to eliminate anything with the auto-scan feature that is not working as it should. YMMV.
If that doesn't work, time to call your local OTA providers to see what's up with their feeds.
I have a samsung smart tv but am not using that function. NO cable, a cd/dvd player, an antenna. Today, I reset the channels because the picture was acting up a lot. I use the automatic channel set up and the AIR selection. When it gets to abut 60%, it switches to DTV air. I have no network, but there is no selection available for no network and it is set for Xfinity (why I do not know). I used to always get those channels. In fact 2 of them are sub-channels and I can get the first one.