Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
That sounds like a splitter failure. Also remember that adding a splitter in the coax reduces the signal anywhere from 1-3 dB, with 3dB equaling a 50% signal reduction. Try taking the splitter out and feeding it direct into the TV that can't find any channels. If it now finds the channels, replace the splitter, perferably with one that is powered/amplified. I feed my antenna into an 8 port amplified splitter. This way instead of losing a large amount of the signal I get a 1 dB gain per port. I still have issues with a few channels, but if it didn't have the amplifier I'd likely only get half of my channels.
Dan Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.