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
Pulling up 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.
Looks like this was caused by r18979 + r18980, should be fixed in r18991.
That fixed it - closing.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1803