After the recent 'update' to the Live TV app (panel, channel, whatever...), I also lost all of my over-the-air channels on my Roku TV.
Here is what I did to get them back YMMV:
Go to Settings->TV Inputs->Live TV->Manage Channels-> check the "Hide Streaming Channels" box
You might have to rescan the antenna input on your ROKU TV (I had to) to ensure that they are all in your line up.
I haven't found a way to have both the Antenna Channels and Streaming Channels cooperate. since the Live TV app was updated.
Roku 3500X
Roku 4400X
Roku 4661X