There is an active thread relating to this topic, specifically about KSEA Tower on Expert today. However, I thought it might be useful to post something separate with a relevant title so people can find it more easily.
There will be occasions when you’re approaching an airport with a green-coloured label, but when you click on the icon only Ground appears. When this happens on Expert, it means that a glitch is occurring, not that there is no Tower/ATIS.
To overcome this, briefly turn off the WiFi on your device, or flip it into Flight Mode. (On my iPad I do this by double-clicking on the home button, then putting on Flight Mode from there.) The IF app will gradually disconnect, and the moment you’re waiting for is when the ATC/headphones icon in the bottom left turns grey. At this point turn your WiFi back on, and when the app fully reconnects you should now be able to see all open frequencies at your destination.
Before following this tip, please be aware of other traffic around you. If you may come into conflict with something else, go into a hold until you have sorted out your connection to Tower.
If you are close to the cone and get an On Guard message to contact Tower but cannot see that frequency, remain connected to Unicom as we controllers can see that - disconnecting your WiFi so you disappear from our radar and then reappear moments later on final will not be appreciated. You may wish to switch your flight number to NORDO to advise the controller of your connection issue.
However, and this is the most important point, you MUST use your radar to ensure you are not conflicting with other traffic, otherwise you may be ghosted.