Have you tried logging out and logging back in?
Sometimes, if you log in too close to the start of the battle, you don't get the notice. You also are unable to register for a battle if you are inside a dungeon. Other than those two reasons, I do not have any other ideas as to why you would not get the alerts. My Medic is Level 26, and she gets the alerts for Janus and Turnpike just fine.
If the problem persists, you could try sending a report ticket to get someone's attention and ask them to resolve the issue.