When I suspend the computer, on wake up the screens do not turn on. To make the screens work again, I have to change to the TTY1 and then to the graphical session (which is the TTY7 on my system) then the light-locker appears and redirects me to the LightDM login screen. I suspect that something inside Xfce (my guess is Xfce4-session) is turning off the screens just before the suspension and then the Xorg session from LightDM is unable to find a valid screen. It's noticeable as it's possible to access a TTY, set the DISPLAY variable and use xrandr to shows the screen status: no resolution is set, as if something on Xfce unset the displays. Using GNOME with LightDM or GDM, this problem does not happen. Computer model: Lenovo Ideapad 310-14ISK OS: Xubuntu 19.04 using Xubuntu-dev PPA Xfce version: 4.14pre1 CPU: Intel Core i3-6100U GPU: Intel HD Graphics 520 RAM: 8 GB Monitor connections affected: eDP and internal DP (external VGA)
Not a bug in xfce4-session. For more information see: https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/1801609
Did you check the linked bug report? Does the problem happen when not using light-locker?
I checked the link, purging light-locker and installing xfce4-screensaver makes the problem stop happening. This bug seems to affect only my computer with the Intel HD Graphics 520 using modesetting. The computer with Radeon GPU does not have this problem and the same computer using the intel Xorg driver instead of modesetting do not have the problem too.
Thanks for confirming that it is indeed a GPU driver bug. Closing this report.