On Kubuntu 17.10 with latest xpra debs (2.2-r17607-1).
xpra attach ssh:server:101
causes xpra to start. The icon appears in the system tray. Then after a couple of seconds, while xpra reports 'Xpra X11 server version 2.2-r17607 64 bits running on linux Ubuntu 17.10 artful' the icon disappears and Xpra seems to hang.
It does not display any remote window, nor it exits with CTRL-C and can only be killed with kill -9.
Sorry for reporting the same bug twice, got the impression it did not get through. Please look at #1720 that has slightly more details.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1719