Chrome OS 9460.42.0, 59.0.3071.57
Monitor: Acer FT200HQL 19.5-inch HD 1600x900 touch screen monitor  

What steps will reproduce the problem?
(1) Recover or Power wash the device 
(2) Sign in 
(3) Connect ACER FT200HQL monitor via HoHo or Apple Type-C multiport adapter or Anker USB-C CB-C34 adapter 

What is the expected result?
External monitor should not flicker 

What happens instead?
External monitor flickers 
It blinks very quickly so the flickering can not be seen in video/phone

Always reproducible via HoHo/Apple/Anker dongle 
Reproducible on 2 Kevin 
Power wash does not help 

Workaround:
Switch from Internal display to Acer monitor in display settings.

Monitor spec:
http://www.amazon.com/Acer-FT200HQL-19-5-Touchscreen-Monitor/dp/B013SRGYJ2  

I am not sure if it's regression.