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?