Issue
While you try upgrading your Heroku Redis plan using the command, heroku redis:upgrade <addon name> --version <version number> --app <appname> and you get an error stating maintenance_running Cannot upgrade at this time as another update is in progress
Resolution
Following steps helps fix the issue:
Step 1 : You'll have to check if there's any scheduled maintenance for Redis addon. Run heroku redis:info -a <appname>.
Step 2 : If you find that any schedule maintenance exists, it is recommended to run the currently scheduled maintenance first.
Step 3: To run the scheduled maintenance manually, you'll have to follow the steps mentioned here.