Sounds like when you say "two Roku devices", assuming you are talking about two RokuTVs.
Unfortunately, the RokuTV does not appear to allow users to "manually" add OTA/antenna channels. (at least on my Insignia, and reportedly other manufacturers). You might want to try a better antenna that at least will pick up all the available signals (even weak) so they are detected during the channel scan and then adjust the antenna as necessary to tune-in the signal. If you already are using a decent antenna, then may be better idea to get a different TV with a better tuner and allows the manual adding of stations and then attach a standalone HDMI Roku device to the TV for streaming purposes.
This is another reason I prefer using a Roku device attached to a non-smart TV rather than an integrated RokuTV. There have been continuing complaints of this so hopefully a future firmware update will some day allow the manual adding of OTA/Antenna channels to avoid having to perform a channel scan after reorienting an antenna.
