The gstreamer plugin probing code pops up an alert dialog:
The procedure entry point faacEncClose could not be located in the dynamic link library libfaac-0.dll
Sadly, removing the "faac" DLL and plugin from the build list doesn't fix things, the cx_freeze automagic still bundles it... so we'll have to exclude it temporarily until MSYS2 fixes things, or rebuild whatever is needed by hand. PITA.
Solved the easy way:
This dll will get replaced with a non-broken one on the next update, hopefully. And in the meantime, we just won't have faac.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1634