First, doing a reset to get the channels back is not a fix. It's a workaround. The problem will just happen again. This need to be addressed.
As for my issue, it just started tonight on my RokuTV. I noticed 3 of my 4 local channels were missing, completely. Nothing brought them back, not even the rescan.
However, I found that if I went into the Manage Channels menu, Add to Favorites, and navigated to one of the missing channels, it would display the channel on the screen. I could leave it there and watch the channel just fine, after the menu dropped off. So it is not an antenna issue, the tv is obviously getting a good signal.
I will look for a software update tomorrow, but this is a new tv. Does Roku really want me to return it?