We are all synced to the same key. I'm fairly certain everyone else is up to date, I'll double check on friday with our next raid.
It only seems to happen on fights like Toth and Zorn or the tanks when we have the groups split. The Toth and Zorn fight is what's making it look like a proximity thing because when the tanks switch and I have to run around to heal, the other group shows up as new dps on the pop-up. And their dps stops being added when we a fully split again. It's not that they don't ever show up.
I agree it makes no sense with the way the data is obtained, it shouldn't be happening. It's highly unlikely that it could be a network issue, as they all show up on every fight where the groups aren't split. I'll make sure everyone is up to date and post an update this weekend.