You have multiple ATP appliances running in a Combo or Manager only configuration, and need to connect to one SEPM controller.
Starting with ATP 3.1, multiple SEPMs can be configured with multiple ATP or SEDR Manager appliances as long as Group Inclusion is used and each appliance is managing seperate groups on the SEPM domain. This will not work if the SEPMs are sharing the same database.
Note that an Appliance can have multiple connections to a single SEPM if each connection is associated with a separate domain.