After being idle, the screen goes blank and locks as it's configured. When I unlock, the screen goes black. After a few seconds the monitor says it has no signal and goes to sleep.
This has been happening 100% of the time after recent updates.

One time I disconnected the HDMI cable, waited a few seconds, and reconnected the cable. The screen came back on that time. However, in other cases re-plugging the cable does nothing.

I've also tried turning the screen off/on, changing the input to another setting then back to HDMI, and a few other things. None of that has any effect.

This is quite upsetting because the only thing I know to do is to force off the power and reboot.

I've looked around the best I know how, and I don't see anyone else having this trouble with Xubuntu 14.04. Any ideas?

What sort of information would be useful?

I disabled Light Locker in the meantime.