Extensions in Queue can't pick up call

I have a system running freePBX version on Asterisk Version 11.10.0. We are using Grandstream GXP2000 phones (I know they’re a little old but other than a few bugs they seem to work fine) I’m having a problem where when calls ring in to the queue one of the extensions in the queue will try and pick up and the phone won’t pick up the call for anyone in the queue. I can not for the life of me figure out what the problem is. My only guess is that the phones and the version of asterisk we are running are having some kind of compatibility issue. Unfortunately I am far from a SIP expert and so I’m not really sure where to go from here.