Switching to another vt (say vt1 with ctrl-alt-f1) and sitting there for >60 seconds results in
2018-10-27 15:58:00,550 Connection lost 2018-10-27 15:58:00,552 Error: printing disabled: 2018-10-27 15:58:00,552 No module named cups
Sounds like a duplicate of #1880 which I have never been able to reproduce in a Debian Stretch VM and doesn't occur on my systems. Please see wiki/ReportingBugs, maybe you can provide more details that will me reproduce it?
Not heard back, closing. Likely a duplicate of #1880
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2012