Well, I don't know exactly what was happening but I do know that the problem was actually with the Netgear switch. For some reason it wouldn't negotiate a link with anything new, though existing connections still worked, which threw me off a bit. Rebooted the switch and now I'm able to negotiate a link with the Grandstream ATA. Also, after rebooting the switch the strange issue of all my ports blinking during a call also stopped.

Strange things were afoot. But all is well now, and no issues with the ATA.