This issue was resolved in the very latest release. UI3-215 and Blue Iris 5.5.7.9. If anyone still encounters this problem after updating, please paste the camera short name for any affected camera in a message to me.
Note it is also possible to get the same symptom if you have disabled webcasting for a particular camera. It will still appear in groups but clicking it won't do anything. That is normal behavior, but it is a very uncommon setup.