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.
Try removing the channel from the Roku home screen by navigating to the channel tile, pressing the * key on your remote and choosing 'Remove channel'. Then restart your device from Settings>System>System restart. Once your player starts up again, add the channel back once more.
I’m not sure if this will help, but I’m gonna put this out there. I was having a similar issue. I was showing 98% signal strength but horrible quality. I attenuated the signal down to about 90% and my quality went almost perfect. All 5 of my Roku now play my OTA without issue.
Let me tell you what I have figured out. The HDHomerun outputs the broadcast signal if it's receiving over the air without transcoding. Broadcast TV in the US is MPEG2 video with Dolby AC3 audio. I have two Roku devices, an Ultra and an Express. The Ultra can decode MPEG2 but not Dolby, the Express cannot decode either. The audio is easy enough to work around, set it to pass the audio in its native form, all TV's in the US can decode Dolby AC3. The video doesn't have a workaround, it's just not going to work unless Roku updates firmware to make it work. Note that as far as I know all decoders that work with MPEG4 AVC are capable of MPEG2 if it's enabled, but clearly it's not enabled on the Express. Likewise Dolby AC3 isn't special, but it does require specific support and the manufacturer must pay a royalty to Dolby. If, like me, you find that having over the air TV is important it's best to get another device for it. I believe that any Android device (Chromecast with Google TV was my choice) will work. Mine works very well, much better than the Ultra which does work, but the controls are very rough, somehow the control API is unreliable.