I've seen this in two battlezones (of three) this week. The other Planet Killers work fine, but the Beta one (Klingon weapons?) the shield does not go down, no matter how long you wait (until the timer runs out for killing the Planet Killers).
It is indeed the Beta Planet Killer. The Klingon weapon never destroys the protective bubble. This has happened before to one of the others and usually starts working again after server restart.
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At 7000MB that's unlikely.