I can confirm that renaming /etc/xdg/autostart/at-spi-dbus-bus.desktop to /etc/xdg/autostart/at-spi-dbus-bus.disabled fixed the issue for me as well.
Lenovo ThinkPad E550 with 2 external monitors running 0.4 Loki. Problem only ever surfaced on cold boot, not on log out/in or restart.
I can confirm that renaming /etc/xdg/ autostart/ at-spi- dbus-bus. desktop to /etc/xdg/ autostart/ at-spi- dbus-bus. disabled fixed the issue for me as well.
Lenovo ThinkPad E550 with 2 external monitors running 0.4 Loki. Problem only ever surfaced on cold boot, not on log out/in or restart.