Hello,
I'm experiencing the same problem reported by Swiss Julian; same configuration (Surface Dock2, Surface pro 7) but with a DELLU2715H monitor.
The USB-C/HDMI connection works if connected directly on my surface pro 7, but no signal when connected to the Surface Dock2.
I hope that the appropriate team at Microsoft are working to fix this issue and I want to remark that we aren't talking about a secondary problem that occurs for a particular configuration or mode of use. We are talking about making two of the newest Microsoft devices work.
I want to point out also that Swiss Julian had spent a lot of his time and without receiving real support. Alone he found a solution that is not practicable in any case as it requires an additional expense (double in the case of two monitors).
Regards,
Mario