SQL Server 2014 Always on listener on named instance for default port
This is happening because you have configured LAB03 listener to listen on port 1433 which is default port of default SQL Server instance, that is why when you connect using the listener it is connecting to SQL Server which is listening on port 1433. While Microsoft allows you to use default port 1433 for listener but this is not a correct thing to do specially when you have multiple instances and listeners. To get around this problem you have to change the port number of listener VT-DB-LAB03
sqllab04\inst02 - sqllab05\inst02 - Listener VT-DB-LAB03 (port 1433)

You can choose free port and configure listener to listen on this port after you do so the issue will resolve.
If you are choosing a non default port for listener you would have to use port number in connection string
Quoting from Docs.Microsoft

Also, since each availability group listener will have a separate virtual network name, each availability group listener configured on a single WSFC can be configured to reference the same default port of 1433.
You can also designate a non-standard listener port; however this
means that you will also need to explicitly specify a target port in
your connection string whenever connecting to the availability group
listener. You will also need to open permission on the firewall for
the non-standard port.
If you use the default port of 1433 for availability group listener
VNNs, you will still need to ensure that no other services on the
cluster node are using this port; otherwise this would cause a port
conflict.

I suggest you also read AlwaysOn Availability Groups, Listener, Named Instances, Port Numbers, etc.