1. Do all of the friends have access to the same expansions? (this might include buying an expansion)
2. Do all of them use the same version? - Only users with the same version (updated version) of the game can play with each other. All of them should check for available updates.
3. Try to manually log out and back in again - Click on your avatar in the main menu, choose the option log out, then log back in again
4. If on Android, try to clear the app’s cache