Random call drops and strange behaviour on Snom 300 handsets

Hi FreePBX experts,

We are experiencing some extremely strange behaviour with a FreePBX installation at one of our clients and are looking for some guidance on how to continue troubleshooting.

The issues reported by users are random call drops (The logs show Hang Up Call) and occasionally when a call is answered from the handset by picking up the receiver the call will instead be put on speakerphone.

The version of FreePBX in use is
The system is in a 1-1 NAT relationship with a PFsense firewall which also has traffic shaping configured to ensure that sufficient bandwidth is always available.
The type of connection is a 20Mbps leased line and we have confirmed using ntopng that the issue is not due to a loss of bandwidth or other latency.
The Free PBX box in question is deployed on a VMware Vsphere 5.5 Infrastructure with 4 Virtual CPU’s available 4GB of RAM and a 200GB Volume.
All of the phones are on a totally separate switch, on a totally separate IP range.

Unfortunately I am quite new to FreePBX, however this set up is more or less identical to the one that we have in our office with the exception that we are using XenServer for virtualisation. We do not experience any issues of this kind on our own internal set up.

Unfortunately since the logs do not seem to indicate any kind of fault I am now at a loss to know how to further diagnose this issue. I would be very grateful if someone could point me in the right direction of how to go about further troubleshooting this issue before I tear the rest of my hair out! :slight_smile: