After upgrading Client from 2.5 to 3.0.6, I am experiencing problems with multiple-screen setup that were not before there. Typically I have two external screens and one laptop screen and sometimes child window menus (e.g. right-click on terminator) appear in different screen than the child window. Sometimes maximizing a child window in certain screen moves it to another screen. I am sorry not being able to provide more information but perhaps this ticket helps in paying attention to possible causes.
Client OS: Windows 10 Pro 1809 17763.973 Server OS: RHEL 7 XPra Server version: 2.5.3 1.r23270.el7_6
The problem occurred with Python3 build of the 3.0.6 Client. I switched now to Python2 build of the 3.0.6 client and there seems to be less problems.
#2703 sounds like a duplicate of this bug.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2595