Applies packet loss concealment and comfort noise generation.cng_plc performs packet loss concealment on lost packets and execute on originate. It is like execute on answer, etc. but only for outbound calls during originate. Comfort noise is artificially generated noise to assure the caller that the call has not disconnected and is being processed.
When experiencing intermittent dropped packets, it could be that the packets are probably late and being dropped and replaced with silence.
You can try 2 things:
run the app cng_plc before bridge and in execute_on_originate on the B-leg.
enable the jitter buffer at a small value by setting jitterbuffer_msec=60