Changing Domain Names

We are going to be changing our domain name next year due to federal requirements. We must move to a .gov domain name in order to communicate with state and federal agencies. Our AD domain name will change...
AD Sync Utility stops on the step "Sending data to Sophos Central to determine changes that would be applied

Clicking on Validate Credentials shows "Credentials are Correct" And the XG Firewall shows no traffic being blocked. Tried it with and without Proxy... no difference it always stops at the same step...