There are several causes of syncs, however, I’m not getting a full sync when changing network settings. I do see it “Updating” the VPG status. I’m running 4.0 U2.
Here is list of causes for re-syncs. http://s3.amazonaws.com/zertodownload_docs/Latest/Zerto%20Virtual%20Replication%20Zerto%20Virtual%20Manager%20%28ZVM%29%20-%20vSphere%20Online%20Help/index.html#page/AdministratorforZertoVirtualManager%2FManageVPG_VC.08.17.html