Outgoing audio stops in middle of call?

I’m having a customer that is having outgoing audio stop in the middle of a call. After 10 minutes the caller can no longer hear the callee using the FreePBX system. Any idea why audio would stop in one direction in the middle of the call? I rean a wireshark and see no huge issues packet wise. We are running through a known router that does not have SIP ALG installed. Thanks