For reference my client and server are Fedora 26 machines running trunk r18990 built from source.
When I first spin up a server and client I get no audio. However I don't get any relevant tracebacks, but upon initial connection both the server and client print:
2018-04-05 09:34:24,844 sound output Warning: failed to identify the pulseaudio default device to use 2018-04-05 09:34:24,844 sound output list indices must be integers, not str
pavucontrol on the server shows that the recording device on the server is set to the wrong device. As a quick workaround you can select
Monitor of Xpra Speaker under recording device and get your sound back.
That fixed it - closing.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1803