It seems that PLC is connected to our server. if the system goes to passive and active mode periodically, there should be some reasons, 1. The internet connection of PLC or your PC is poor 2. The PLC can be reset by itself because of runtime program or external 24VDC power supply problem.
So, I suggest you to check power supply of PLC and check internet connection of PLC and PC and make very simple program for Scada and PLC ladder and try.