Calls intermittently going directly to voicemail

[lost_]

Callers were getting fast busy on incoming calls to my add-on line today from around noon for a few hours. Outgoing calls were ok, and rebooting the ATA didn't solve it, though the vpanel showed the device registered to East. My primary line worked fine during that time.

EDIT: VM is disabled on my add-on line. I wonder if it would've gone to it instead of fast busy.