No audio on some WebRTC outbound calls

[Ferg]

I have the softphone plugin set up and successfully taking inbound calls, but on some outbound calls the softphone doesn't send or receive audio from the PBX. When I check the call recording it only has audio from the external recipient.

[Ferg]

When I tried to search for solutions, they tend to say that it's a NAT issue, but none of the suggested solutions have worked. I'm using FreePBX, and I've tried different web browsers. Is there something other than a NAT issue that could be causing it?