GTM not acquire the Virtual Server of LTM

The issue that the solution describes pertains to the LTM virtual servers themselves.

So you have an internal network between your GTM and your LTMs that they communicate over. Is it accurate to say that your GTM doesn't provide these internal network addresses associated with your LTM virtual servers to external clients that are querying it? Client queries should be answered with an external address which is translated somewhere in your network, possibly on a firewall. If this is the case, then the known issue I linked above could still be the problem.