Here's what I see on mine when something like that happens:

2016-12-21 23:15:08.885445 [NOTICE] switch_channel.c:1104 New Channel sofia/internal/3407@10.100.1.2:5060 [abcc54a5-e4b9-405e-a1a5-90036b05356a]
2016-12-21 23:15:08.885445 [DEBUG] switch_core_state_machine.c:584 (sofia/internal/3407@10.100.1.2:5060) Running State Change CS_NEW (Cur 1 Tot 74)
2016-12-21 23:15:08.885445 [DEBUG] sofia.c:9746 sofia/internal/3407@10.100.1.2:5060 receiving invite from 158.69.243.194:5071 version: 1.6.13 git e755b43 2016-11-29 15:46:39Z 64bit
2016-12-21 23:15:08.885445 [DEBUG] sofia.c:9913 IP 158.69.243.194 Rejected by acl "domains". Falling back to Digest auth.