Have you created a Tubi account and signed in? You can use Tubi without an account but it might help.
The problem is it is happening to people who are signed in. I have uninstalled and reinstalled Tubi. I not the person that asked the question but experiencing the same thing. I am signed in on my Roku TV, have logged out, back in, uninstalled and reinstalled the app. I plan to reach out to Tubi, if I get a response I will post it here.
After removing the channel, but BEFORE reinstalling it, did you RESTART** your Roku to clear its memory cache? Without the restart you may not get a clean reinstall. This is not a cure-all but at least it will assure you of having an uncorrupted copy of the current channel app.
Depending on your Roku model number you'll find the "System restart" option under either "Settings > System > Power" or under "Settings > System". If you don't have sufficient control to use the menus, or if it is just more convenient, you can also restart by pulling the power plug for a short while, then plugging it back in.
**On a Roku TV with "Fast TV Start" enabled, turning the TV off/on only puts you in/out of a low power standby state, it does NOT give you a complete restart. Use the methods above.