Tested both the Acer Chromebook 14 for Work and the HP Chromebook 13 G1 with the UD-CA1. Each is brand new and running Chrome OS:
Version 57.0.2987.123 (64-bit)
Platform 9202.56.1 (Official Build) stable-channel chell
ARC Version 3831942
The issue I’m going to describe also occurred with the prior version of Chrome OS.
Approximately 80% of the time, the Chromebook hangs when it goes into sleep mode other times it’s fine. When this happens, the external monitor connected directly to the Chromebook still displays the Chromebook desktop while the Chromebook and external display connected to the docking station are blank. The only way to resume is to do a hard shutdown and restart. This issue only occurs when connected to the UD-CA1.