Adtran 706 cannot receive inbound calls through AA50

We have two Adtran 706’s on a Digium AA50. One is on site, the other remote – accessing the AA50 on a public network.

Both can dial out with no problem. Incoming calling, both inside and outside the network, is the problem. Incoming calls only work right after reset. Then after a short period of time (maybe 5 minutes) calls go to voicemail, with no ringtone heard during the call by the caller or on the 706. Sometimes calling using extensions works, sometimes not.

4 Linksys 922’s work just fine using the AA50. A 2nd line on the Adtran 706 is provisioned directly to switch (bypassing the AA50). This line works fine.

It is the 706’s interaction with the AA50 that seems to be the problem. Has anyone encountered this issue? What was your fix?