I also found this bug using the HWE stack.
System76 Lemur 6 (i7-6500U CPU Skylake GT2 HD520) running 16.04.3 LTS
Flicker occurs on return from black monitor to screens after screen has
been turned off. Worse with a second monitor plugged in. Resolution is
to click on the workplace switcher and then select a screen (1/4).
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Black flicker when leaving monitor
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