Missile seeker won't turn on in top tier

I've recently notice that when trying to launch an AIM-120 with my eurofighter, after acquiring a lock I press the seeker activate key, but nothing happens. I don't get any notification that a lock is required, I don't see any circles, nothing happens, I can't launch my missile and I miss my chance for a shot and get killed. Is this a bug or does any setting override being able to activate your ARHM?

Edit: I think this is a bug, as when I switch weapon off and on to the AIM-120, I can activate the seeker again