Xubuntu: screen does not wake up after being locked

[Charles]

I run Xubuntu on a Dell Latitude E6530 laptop with Intel graphics.

Ever since upgrading to 18.10 cosmic, the screen remains blank (and powered off) after being locked. Moving the mouse or pressing keys on the keyboard does not turn the screen back on. I found, more or less by accident, that switching to another virtual terminal (Ctrl+Alt+F1) and back will turn the screen back on and allow me to log in again. But this doesn't always work and sometimes after suspend/resume I have to hard-reset the machine in order to use it again.

Any ideas what might be wrong? Some googling leads me to believe that this might be something to do with Light Locker but I don't know how to troubleshoot that.

$ sudo lshw -class display
  *-display
       description: VGA compatible controller
       product: 3rd Gen Core processor Graphics Controller
       vendor: Intel Corporation
       physical id: 2
       bus info: pci@0000:00:02.0
       version: 09
       width: 64 bits
       clock: 33MHz
       capabilities: msi pm vga_controller bus_master cap_list rom
       configuration: driver=i915 latency=0
       resources: irq:29 memory:f6400000-f67fffff memory:e0000000-efffffff ioport:f000(size=64) memory:c0000-dffff

What other diagnostic information can I provide?

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. It seems that your bug report is not filed about a specific source package though, rather it is just filed against Ubuntu in general. It is important that bug reports be filed about source packages so that people interested in the package can find the bugs about it. You can find some hints about determining what package your bug might be about at https://wiki.ubuntu.com/Bugs/FindRightPackage. You might also ask for help in the #ubuntu-bugs irc channel on Freenode.

To change the source package that this bug is filed about visit https://bugs.launchpad.net/ubuntu/+bug/1804235/+editstatus and add the package name in the text box next to the word Package.

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