Hi MSB59,
Welcome to the Roku Community!
Thanks for reaching out about this issue you're having with the Discovery Plus channel. We'd like to assist you. It seems like this device is already in legacy and can no longer support the most recent features. This means that it will no longer hold further updates on channels and software updates. However, as per checking, I see that this device is still supported with the current version of the app. We'd like to know the current build of this channel running on your Roku 3500R
Please share the current build; you can get this by highlighting the channel tile, pressing the * sign button, and then sharing it here.
We would also recommend clicking on the "Check for updates" and see if there's available one.
Regards,
Rey