When resolving the Global Catalog (GC), it is assumed that the name of a sub-domain contains the parent domain. This is normally the case, but not necessarily so.
The setup can also look like this:
domain (<domain2>.<domain1>), parent domain (<domain3>.<domain1>)
When searching for a suitable GC, this combination currently does not lead to any result regarding the DNS resolution of the GC, or the search terminates at the wrong parent domain from which non-resolvable IP addresses for GC servers are supplied.
An enhancement request (#31179) has been created.
The product team will evaluate the request and this feature may become available in a future release of the product.