I'm not able to test at present, as I don't currently have a Roku Express (or Express+) in service. However, NowhereMan is usually very good about ensuring what devices work with his channels. It would surprise me if he made it available for the Roku Express+ (assuming that's the case, since you were able to install it) without ensuring it worked with the device.
Could simply be a glitch. Try removing the channel, rebooting the Roku device, then re-adding the channel.
Basil
https://www.basilsblog.com/
Roku Ultra (4660)
Apple TV (5th gen), TiVo
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Roku boxes from every generation.
Apple TV (2nd, 3rd, 4th gen)