Why is it never changes from jobs. even there is no controller that controlling?

For example if I choose to ATC ground and tower at KUNC, but there is another person coming in at a same time someone was in ground and I couldn’t control ground and it says obs. and even a controller was gone still I couldn’t control that frequency. I think this is a bug.

I see, unfortunately I am not advanced ATC yet coz I can’t take test haha:)

Answer is already in several posts such as this one:

Duplicate topic. Please search before posting. Thanks!