MS SQL Monitoring not working correctly on named instances

MS SQL Monitoring not working correctly on named instances

Afternoon All,

We've an applications Manager monitoring several SQL servers.

Whenever the Monitor has the option "Connect using Named Instance" (See SQL-1.png attached) the monitor will be unavailable most of the time, only being shown as available for 5 minutes or so (see SQL-2.png attached).

I don't think this is the servers themselves as my screenshot includes multiple servers with both named and default instances on it and only the default non-named instances work fine.

Anybody have any ideas?