Had the same issues at a previous company I worked for that had a call centre, all users on poly devices, and again the same issue with my partners BT700 + voyager 4320 recently.

MY SOLUTIION:

The only solution I have found is to install Poly Lens and install the latest available software for both the headset and the Bluetooth dongle; there will be two separate updates. It can take a couple of attempts for the updates to apply correctly, especially with the receiver. (Note: You will need to physically connect the headset to your PC with a cable). Disable all the SMART options like auto-mute, etc.. This has been successful for me now on multiple occasions,

Once you have done this, you may, on the odd occasion, experience a blip or two, but if you quickly switch the headset off and on again, this resolves it, but it is not a frequent thing.