GTM not reflecting status of LTM Virtual Servers

I have 2 Servers configured on GTM. the 2 servers are LTM devices. Each server is in different Data Center and each server has one Virtual Server. When one of these Virtual servers goes down, the status of VS on LTM is down also. But, the down status is not reflected to GTM. Inside the server configured on GTM, the status of the VS is still showing up.

 

Any idea what could be the reason behind that ?