3rd Party MSTP controllers are not able to be discovered.
StruxureWare Building Operation
Automation Server (AS)
MAC address of the Automation Server's MSTP Network was not configured properly.
Under the AS / BACnet Interface / MSTP Network the MAC address had been configured differently to the default value of 0. Change the MSTP Network MAC address from 40 to 0 and 3rd party controllers will be discovered properly.