laptop screen never comes on after undock / sleep / open of laptop

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I've already got apport configured to report everything (i.e., I've already done the workaround suggested in bug 994921), and there is no crash either in /var/crash or on https://errors.ubuntu.com. I don't think a crash is what's happening here.

Additional data:

* If, after I've woken up my laptop and the screen is blank, I put it back in the dock with the lid closed, the dock's two monitors come alive just fine.

* If I then open the laptop lid, the monitors reconfigure themselves and I correctly end up with both the two monitors and the laptop screen all live.

* Ditto if I then close the lid -- the displays reconfigure themselves and only the two dock monitors are enabled.

* If I temporarily disable the udev script that causes the laptop to go to sleep automatically when I undock it, then when I undock it and open the lid the screen comes on just fine.

* When the screen is in the off-but-should-be-on state I've reported here, Ctrl-Alt-F* doesn't switch to a different VTY.

* This problem happens _almost_ every time I undock, but not every time. I've tried it seven or eight times, and one of those times, the screen came on properly when I woke the laptop by opening the lid. All the other times the screen never came on until I either power-cycled or put the laptop back in the dock.

OK. This sounds related to bug 1723025 or one of:

https://bugs.launchpad.net/ubuntu/+source/gdm3/+bugs?field.tag=multimonitor

OK, so, I've learned more about this.

If I wait for like 10-15 seconds after waking the laptop and type ctrl-alt-f1, then after a long delay after that the screen will switch to the GNOME login screen, and then if I select my account and type my password, I am brought back to my previous session. But, there's something weird about the state of things at that point. E.g., if I then put the laptop to sleep and wake it back up again, the lock screen for my session appears, but it won't accept any keyboard or mouse input. To get back into my session I have to do the ctrl-alt-f1 trick again.

If I open the laptop while docked, wait for the built-in screen to activate such that all three monitors are active, then undock and suspend the laptop before gdm3 finishes reconfiguring so that only the laptop screen is active, then I'm in the same boat as the original bug report when I wake up the laptop, i.e., the screen remains black no matter how long I wait, but if I wait a while after waking and then type ctrl-alt-f1 I can proceed as in the previous paragraph.

If I open the laptop while docked, wait for the built-in screen to activate such that all three monitors are active, undock, wait for gdm3 to finish reconfiguring so that only the laptop screen is active, _then_ suspend the laptop, then when I wake the laptop back up the screen does come on.

In short, it appears that the problem is related to suspending the computer when it is in the middle of reconfiguring what its active screens are. It doesn't finish or restart that configuration when it wakes up, so it remains in a weird, messed-up state.

At least, that's my best guess, given the data I've collected.

Was there ever a resolution to this. I am having much the same problem using my Dell Latitude 7480 running Ubuntu 18.04.2 LTS. In my case the behaviour that causes problems is that I have the laptop docked and suspend it - and then undock the laptop. When I attempt to restart the laptop (undocked) I get the same behaviour reported by the OP - i.e. laptop starts up and screen backlight comes on, but nothing is ever displayed. I can switch to a virtual console and use that normally including rebooting. There is nothing in /var/crash or on http://errors.ubuntu.com/ . I have tried killing a range of X related processes to see if I could get the GUI to restart - but without success.

My guess would be that the system isn't coping with the dock (with 2 external monitors) being removed while it is suspended.

Let me know if any further system details would be useful.

Status changed to 'Confirmed' because the bug affects multiple users.

I'm having the same issue (mostly) with Ubuntu 19.04.

I'm using:
WM: i3
DM: LightDM
Dock: Caldigit TS3 Plus with 2 monitors connected through DP daisy chain

If I suspend after undocking, when I resume the screen is blank, but the laptop is not frozen because I can still type in commands and stuff. I can hit my configured shortcut to reboot and it does. For me, attempting to switch to a different TTY does not work. However, when it goes into the reboot sequence, the Ubuntu screen does show up before shutting down.

Forgot to mention, laptop is Thinkpad X1 Carbon 6th gen