House line rings once, then nothing

This started happening to me recently. The house line will ring once on an incoming call, and then just hang up for no reason. It happens maybe 1 out of 10 calls. Here is what the CLI captures during a call that gets hung up on. Any ideas?

-- Executing [s@menu:3] Ringing("SIP/16785551234-081ce4c8", "") in new stack
-- Executing [s@menu:4] WaitExten("SIP/16785551234-081ce4c8", "") in new stack

[Feb 1 10:20:03] WARNING[4222]: chan_sip.c:1881 retrans_pkt: Maximum retries exceeded on transmission 2e1785c2092791ae70c30d232515ae43@64.118.82.164 for seqno 102 (Critical Response)
[Feb 1 10:20:03] WARNING[4222]: chan_sip.c:1898 retrans_pkt: Hanging up call 2e1785c2092791ae70c30d232515ae43@64.118.82.164 - no reply to our critical packet.
== Spawn extension (menu, s, 4) exited non-zero on ‘SIP/16785551234-081ce4c8’
[Feb 1 10:20:03] WARNING[4222]: chan_sip.c:1881 retrans_pkt: Maximum retries exceeded on transmission 2e1785c2092791ae70c30d232515ae43@64.118.82.164 for seqno 102 (Critical Response)
[Feb 1 10:20:04] WARNING[4222]: chan_sip.c:1881 retrans_pkt: Maximum retries exceeded on transmission 2e1785c2092791ae70c30d232515ae43@64.118.82.164 for seqno 102 (Critical Response)
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