No outgoing audio after returning from hold & transfer drops

We are using FreePBX, and have PolyCom SoundPoint IP 321 phones running the latest firmware.

Our former Philippines tech migrated our PBX to a more powerful Amazon instance last Monday, and we have had issues transferring and holding calls since then. He has since left the company due to a severe health problem and is not reachable at this time.

Sometimes, with no discernible pattern, after returning a call from hold or receiving a transferred call, the caller does not hear our microphone but we hear them.

A second issue we are facing is that when a caller is transferred, sometimes the caller is dropped altogether and has to call us back.

Now, the weird thing is that this is only happening in one of our three locations. Our Atlantic office has the same phones with no problems, and our overseas office has different phones with no problems. I thought it was our phones but I have not been able to resolve it with any amount of configuration or reviewing of log files. Despite the localization of the problem, somebody with more experience offered the comment ‘it sounds like a PBX problem’.

Can somebody here please weigh in? We are in the telecom industry and this has a severe effect on our image with customers.