I don't work for JRiver, so I can't directly help with restores. The staff is usually really good about resetting the restore count though, especially when it's because of them not working correctly.
Those license files are good for 14 days, so you can use the same MJR file more than once during that time period.
When you install MC21, you might try doing the restore directly from MC21 itself. That seems to be the most reliable way to make sure the license gets installed. Good luck!
Brian.