so if it 2 just talking, can you eliminate those 2 as a test, and have others try to talk from their locations to see if all users have similar problems.
Also, if you set bbb to record on server., what does the recorded audio sound like? is the audio clear in recording? Or do you hear the defects in recording.
If your missing syllables on start of active talker, its possible to lower energy level on freeswitch conference for voice activity detection, but your recording did not sound like that.
Also, assume your server is a 100mb symmetrical internet connection and bandwidth is good. Although for 2 talker to 20participants not much is needed.
You can also look at chrome://webrtc-internals/ and see detailed info on the packet and jitter that may be occuring in the network at the user level.
And lastly give
demo.bigbluebutton.org a try to see how it sounds (there will be latency, but audio quality should be good)
regards,
Stephen