Comment 10 for bug 1615734

to add my two cents: the situation is totally different for users which plug in their displays directly into the notebook's ports and users trying to use the outputs of one of the docking stations.
According to my prior research for this problem this is caused by Lenovo not using simply pass-through connectors via the docking port anymore, but instead they are now using a single DisplayPort MST (MultiStreamTransort) connection to the dock, where a DisplayPort MST Hub splits the signals to the various outputs (converting them also in case of VGA out).

MST support seems to work fine only for some (4K) displays which report 2 panels with half the resolution each via DP, but not for those hubs atm, sadly. Maybe it works with the newest kernel and (as of yet unreleased) nouveau driver.
So the issues with directly plugging in displays should not be confused.

Other than that:
NVidia Driver 378 (currently newest release)
Linux 4.10.1 (mainline)
Bios revision: 1.38

But even with all the newest releases, still no improvement versus 4.4 kernel and recommended nvidia version...
Although if I am very lucky, I may be able to boot with two external displays attached which may sort of work, but then the desktop on the rightmost display is always panning for some reason and hotplugging anything (removing notebook from dock or simply unplugging a display) leads to the issue described by OP again. So my dock is for now simply being used as a VERY expensive USB (and power) hub ;)