That is the strangest issue I've heard with a premium streaming app. A factory reset may not have been enough since the channel exists on your account on the Roku server and not on your device, and if this is a cache issue then it could just present itself after reloading back on your device. So if you haven't done this already, try to log out of Discovery Plus on your Roku device, remove the channel, restart the Roku, then try to change the time zone of the Roku up six hours, restart the Roku, then change it back six hours, restart the Roku, add the channel, and log back in.
If that doesn't work, you need to contact Discovery Plus and let them know this is happening to your Roku model. Let them know that you factory reset the Roku so they know it's not your device and that you tried to log out, remove, restart, change the timezone up and back, and add the channel which didn't work. Since your phone app is working fine then this isn't an account issue, so let customer service know this detail. If your phone is on the same network as your Roku and you're not using mobile internet, let them know that too because they may otherwise want to troubleshoot your network. Also, let them know what time zone your Roku is in because that may have somehow gotten messed up with that Discovery Plus Roku app on their end.
I wouldn't know if my Roku devices were also affected because I don't subscribe to this channel, but if this issue is specific to this Roku model, they may be able to patch this while on the phone with you. Make sure to get a support ticket so you can quickly refer back to this if you have to contact them again. Perhaps others who have this issue will reply to this thread, and they too can contact customer support to help resolve this.
In the meantime, until this is resolved, if you have a computer or tablet, you can remotely connect that to the Roku and watch Discovery Plus that way. You probably could connect your phone to your Roku, but that's a pain if you receive a phone call.
