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.
Does this clear up the issue you are seeing? Please keep us posted.
I tried removing and reinstalling the app. No change. I did see in this forum on other issues that the recommendation was to disable the "Airtime Fairness" in the wireless section of home routers.
I disabled it on my router and that has fixed the problem.
Interestingly in addition to allowing the login to the app taking place it also stopped the network errors I was getting when this app was trying to load its content of what tennis matches were available to watch.
If putting off the channel and including it back after you've restarted the tool does no longer resolve the channel problem, I'd propose accomplishing out to the channel aid at once to document the difficulty and request extra guide.