regarding your first question: I don't know your role, that means I cannot give you any answer if something is in scope or out of scope. If someone else is managing the network setup, they should be able to give you recommendations/hints what to change on your side to make it work (again).
and the second question: Can you be more specific? There are a number of issues which can be related to replication, but I am quite sure that some general answers to that question do not help you.
If you need a proxy in replication, disabling the proxy support will effectively disable your replication, because the network connection cannot be made. If there's no need to use a proxy, the connection can be made without proxy, and disabling the proxy will not have any effect.
When we saw this issue, we found the Proxy setting was Enabled due to some XYZ reason(not sure), but it start failing the request of replication as TMG settings(who does proxy policy settings) they changed the policy so all the request going to replication server was getting failed.
So what change in configuration we have done is,we added the server list in No proxy list which gave Test Connection successful for the replication.
So Joerg i want to know 2 things now:
=>Proxy setting policy setting is something which is out of our scope??TMG is vendor who does that change.
=>what are the list of issues majorly occurs in Replication?