I also have a surface pro 3 with windows 10 hooked up to 2 external monitors and have the same issue.
Fun fact: when I was having this problem, I had the second monitor plugged into the dock. I would get a failure in as little as 20 minutes.
Right now, I have the second monitor plugged directly into the port on the Surface 3, and it's gone several days without a failure. This suggests that the issue is related to how the video feeds through the dock (presumably through the connectors on the bottom of the Surface).
Try not having a monitor on the dock -- those with two extras, unplug the one. Those with only one extra, try the other port. I'd like to know if other people see similar results. That should at least narrow things down.