Missing first 5 seconds of audio

[night1]

I'm having an issue with all inbound calls missing the first 3-5 seconds of audio BUT if you hang up and call right back the audio is not missing, if you wait about 3 minutes to call back the first 3-5 seconds of audio is missing again.

Have checked with Vitelity and they do not see an issue

tested this on a Windows and Linux deployment
Firewall checker has no issues.

Thoughts?
Thanks,

 

[mixig]

Make that two calls, with and without audio at the begining of the call, analyze both of them with wireshark and see is audio is really missing; what is happening after you provider sends ACK message to your PBX (you can see by time stamp in wireshark is there a problem with your provider, does audio coming right after ACK).
If everything is OK try the same on the LAN interface.
Also is there a missing audio in one way or two way?

 

[sip.bg]

Looks like a network issue, check ping time, packet loss, jitter, latency.
pathping <PBX_IP_address> is an useful command (Microsoft Command Prompt), run from a PC in the network with phones.