We implemented some changes awhile back that requires each device to contain a secret now, I did not have access to every device to actually test the changes, but the effort was made to ensure they were all updated. It is entirely possible your device is not actually registered, though your MD should be.
Please verify that the extension assigned to the grandstream shows as a registered extension in Asterisk CLI with sip show peers.
Here's what I have. It doesn't look like the MD or the Grandstream aren't registered. Any thoughts?
Name/username Host Dyn Nat ACL Port Status
broadvoice/<my number> <IP_Address> N 5060 Unmonitored
202/202 (Unspecified) D N 0 UNKNOWN
201/201 (Unspecified) D N 0 UNKNOWN
200/200 192.168.80.1 D N 5061 OK (4 ms)
4 sip peers [Monitored: 1 online, 2 offline Unmonitored: 1 online, 0 offline]