Ubuntu dual displays lose signal, main laptop display goes inactive/non responsive when log out?

Question

I am running Ubuntu 18.04 and I have two identical external displays(LG) which are connected to my laptop. One through HDMI directly, the other display is connected by VGA. I'm experiencing a couple of issues with this setup:

1. When both displays are plugged in and when I log out/close laptop lid both displays lose signal and the main laptop display becomes unresponsive (purple screen with mouse icon which doesn't react).

2. Additionally, when I try to restart the laptop and either of the monitors are connected, the laptop display will return to the unresponsive display state.

To correct either of these, I need to first disconnect all external displays, restart the laptop then connect the HDMI display followed by the VGA display(in that order).

The displays worked perfectly until a couple of days ago, the only change I made to the system was to edit

sudo -H gedit /etc/default/grub

specifically, changing the setting:

GRUB_CMDLINE_LINUX="acpi=force irqpoll"

then updating the GRUB.

I have gone as far as to delete my ~/.config/monitor.xml files, including the untiy-monitor.xml files to no avail.

Edit: Another odd behaviour is that when I go to Settings -> Devices -> Screen Display and make a change then apply those changes all the screens go inactive as usual.

Answer 1

I suffer from a similar issue on Ubuntu 18.04 (when Windows 10 is booted everything is fine). I have two external displays chained by PD and then connected to my laptop by a mPD. After log-in the laptop's built-in display becomes unresponsive (purple screen with mouse icon which doesn't react), just as in your case. As I work on the external display, I simplty ignored the unresponsive built-in one ;P However, one of the external displays goes black (sleeping mode). To wake it up I use

$ xset dpms force off

Unfortunately, if I boot without the external displays, the built-in display becomes unresponsive (purple screen with mouse icon which doesn't react) just after login. To switch it, I had to enable (or disable) the following:

BIOS -> Video -> Switchable Graphics -> (dis)enable:
-Discrete Graphics Controller Direct Output Mode,
-Switchable Graphics,
-Dock Display Port through Integrated