Плавающая проблема [asterisk + freepbx]

Доброго дня. Исходные данные:

• Freepbx 13 + asterisk 13.6.0 в ДЦ с белым IP.
• Канальный модуль pjsip.
• Mikrotik в офисе и клиенты cisco spa303 (прошивка 7.5.7s) за nat.

В промежутке рабочего дня начали возникать проблемы с рядом аппаратов, телефоны не проходят регистрацию (в веб-интерфейсе ошибка "Failed - No Response").

Все это ровно до перезагрузки mikrotik. При этом проблем с прохождением голоса и звонками не наблюдается.

Вырезка из дебага со стороны asterisk:

<--- Received SIP request (479 bytes) from UDP:87.249.39.x:1025 --->
REGISTER sip:85.192.13.x:5061 SIP/2.0
Via: SIP/2.0/UDP 192.168.80.248:5061;branch=z9hG4bK-2a3477c8
From: "112" <sip:112@85.192.13.x>;tag=debc3b5fccaba21bo0
To: "112" <sip:112@85.192.13.x>
Call-ID: ce3fda4d-bc53daef@192.168.80.248
CSeq: 1685 REGISTER
Max-Forwards: 70
Contact: "112" <sip:112@192.168.80.248:5061>;expires=3600
User-Agent: Cisco/SPA303-7.5.7s
Content-Length: 0
Allow: ACK, BYE, CANCEL, INFO, INVITE, NOTIFY, OPTIONS, REFER, UPDATE
Supported: replaces


<--- Transmitting SIP response (490 bytes) to UDP:87.249.39.x:5061 --->
SIP/2.0 401 Unauthorized
Via: SIP/2.0/UDP 192.168.80.248:5061;received=87.249.39.x;branch=z9hG4bK-2a3477c8
Call-ID: ce3fda4d-bc53daef@192.168.80.248
From: "112" <sip:112@85.192.13.x>;tag=debc3b5fccaba21bo0
To: "112" <sip:112@85.192.13.x>;tag=z9hG4bK-2a3477c8
CSeq: 1685 REGISTER
WWW-Authenticate: Digest  realm="asterisk",nonce="1492093522/3242a043e48ce34ac8fb591644548c33",opaque="5331fded5043bb22",algorithm=md5,qop="auth"
Server: FPBX-13.0.190.19(13.6.0)
Content-Length:  0

Снял дополнительно дебаг с самого аппарата:

Apr 13 19:56:28 192.168.80.248
Apr 13 19:56:28 192.168.80.248
Apr 13 19:56:32 192.168.80.248 [0: 5061]->85.192.13.x:5061{479)
Apr 13 19:56:32 192.168.80.248 [0: 5061]->85.192.13.x:5061{479)
Apr 13 19:56:32 REGISTER sip: 85.192.13.x:5061 SIP/2.0#015#012Via: SIP/2.0/UDP 192.168.80.248:5061;branch=z9hG4bK-a41a57a6#015#012From: "112" <sip:112@85.192.13.x>;tag=41e3e692c55f3b33o0#015#012To: "112" <sip:112@85.192.13.x>#015#012Call-ID: ce3fda4d-bc53daef@192.168.80.248#015#012CSeq: 2128 REGISTER#015#012Max-Forwards: 70#015#012Contact: "112" <sip:112@192.168.80.248:5061>;expires=3600#015#012User-Agent: Cisco/SPA303-7.5.7s#015#012Content-Length: 0#015#012Allow: ACK, BYE, CANCEL, INFO, INVITE, NOTIFY, OPTIONS, REFER, UPDATE#015#012Supported: replaces#015#012#015
Apr 13 19:56:32 192.168.80.248
Apr 13 19:56:32 192.168.80.248
Apr 13 19:56:36 192.168.80.248 [0: 5061]->85.192.13.x:5061{479)
Apr 13 19:56:36 192.168.80.248 [0: 5061]->85.192.13.x:5061{479)
Apr 13 19:56:36 REGISTER sip: 85.192.13.x:5061 SIP/2.0#015#012Via: SIP/2.0/UDP 192.168.80.248:5061;branch=z9hG4bK-a41a57a6#015#012From: "112" <sip:112@85.192.13.x>;tag=41e3e692c55f3b33o0#015#012To: "112" <sip:112@85.192.13.x>#015#012Call-ID: ce3fda4d-bc53daef@192.168.80.248#015#012CSeq: 2128 REGISTER#015#012Max-Forwards: 70#015#012Contact: "112" <sip:112@192.168.80.248:5061>;expires=3600#015#012User-Agent: Cisco/SPA303-7.5.7s#015#012Content-Length: 0#015#012Allow: ACK, BYE, CANCEL, INFO, INVITE, NOTIFY, OPTIONS, REFER, UPDATE#015#012Supported: replaces#015#012#015
Apr 13 19:56:36 192.168.80.248
Apr 13 19:56:36 192.168.80.248
Apr 13 19:56:37 tryAltIp 0 0
Apr 13 19:56:37 192.168.80.248 #### reg_or_retry 0
Apr 13 19:56:37 tryAltIp return ERROR 2
Apr 13 19:56:37 SIP_regTsEventProc 4
Apr 13 19:56:37 192.168.80.248 [0]SIP: RegFailed;Retry in 30s
Apr 13 19:56:37 192.168.80.248 [0]SIP: RegFailed;Retry in 30s
Apr 13 19:56:37 192.168.80.248 RSE_DEBUG: rse_unref context: 0x949c0de4
Apr 13 19:56:37 SIP_regTsEventProc 31

И так покругу