MSTP controllers go offline when changing the MaxMaster value in the Automation Server from it's default of 127.
Andover Continuum, TAC I/A Series, SmartStruxure Solution, SmartStruxure Lite
The maxmaster value is being set lower than some or all of the MSTP controllers on the network.
The value for maxmaster needs to be at least one greater than the highest addressed MSTP node id. If your last node is MAC id=54 then your maxmaster will need to be set to 55 or higher.