RDS - Server 2016 and how to test where it's broken

We have a brand new RDS environment on Server 2016.  It was set up by Microsoft who came onsite to help us.  It worked great.

THEN - some genius IT director decided our gateway servers need to be in a DMZ.  

Now, it doesn't work and I need help finding out why.

What ports are needed from the gateway server to the Connection broker?  I currently have 443 and 3389 open from the gateway servers to the connection brokers.

The gateway servers are pointed to a load balanced VIP in front of our two connection brokers.

My network guy tells me it's all configured correctly, but the only thing that changed was that the two gateway servers moved to a DMZ.  Nothing in the config of the deployment changed.

Anyway, how do I go about troubleshooting this please?

Thanks

Cliff