OPC toolbox is invalid when I start the program

Hello. I'm using OPC toolbox to communicate my MATLAB program with PLC. I'm controlling several variables by PLC and then I'm sending them threw OPC to the MATLAB, where the whole simulation runs. The problem is, when the simulation starts, OPC toolbox starts to be invalid, but after few seconds, respectively it will read the first value of variable in PLC and then it will write that OPC toolbox is invalid. Here is my OPC configuration.

classdef MatlabPLC < handle
    properties
        WE;
       opcData;
       a; %OPC server
    end
       methods
           function this = MatlabPLC()             
               this.WE = false;
               if mpcchecktoolboxinstalled('opc')
                   opcreset
                   clear mpcopcPlatnStep;
                   clear mpcopcMPCstep;
                   try
                       this.a = opcda('192.168.0.101','Kepware.KEPServerEX.V6');
                       connect(this.a)
                       catch ME
                       disp('The Kepware.KEPServerEX.V6 must be running on the local machine.')
                       return
                   end
               end
               svetla = addgroup(this.a);
               this.opcData.WE = additem(svetla,'SIEMENS.s7-1200.svetla.WE'); 
           end
           function delete(this)
               %destruktor
               disconnect(this.a);
           end
  % WEST - EAST (GETTER + SETTER)         
           function WE = getWE(this)
               pom = read(this.opcData.WE);
               this.WE = pom.Value;
               WE = this.WE;
           end
           function setWE(this, WE)
               this.WE = WE;
               write(this.opcData.WE, this.WE);
           end                  
       end
end
                   

variable WE is boolean. The problem begin, when I call getter(getWE) in my script. Then the OPC fall down. Does anyone know whats wrong? If there is a manual how to correctly connect MATLAB(not simulink) with PLC threw OPC, I will be very thankful.