Per https://codesearch.wmcloud.org/search/?q=api.svc.(eqiad%7Ccodfw).wmnet&i=nope&files=&excludeFiles=&repos= various services hardcode api.svc.eqiad.wmnet in their configuration instead of using discovery DNS.
This seems like it's an issue for Datacenter-Switchover but it's unclear why this hasn't been an issue before.