Cannot write property value to Kepware in the remote thing

Hi,

I got a very strange phenomenon.  I have a remote thing which is bound to the data tag of Kepware, when kepware detect the change of PLC,  the data change event of the property in Thingworx will trigger the subscription to update the same property, but it doesn't take effect , the property in Thingworx still remain unchanged ,  and there is no error found.  But if manually change the data tag in Kepware or using timer then it works.  

In a summery : 

• PLC -> update Kepware data tag -> raise data change event in Thingworx -> trigger subscription -> execute sync service to update the property value  ==>  does NOT work . no effect  
• manually update Kepware data tag -> raise data change event in Thingworx -> trigger subscription -> execute sync service to update the property value  ==>  works 
•  PLC -> update Kepware data tag -> launch a timer to poll the property value -> execute the same sync service to update the property value    ==> works 
•  PLC -> update Kepware data tag -> launch a timer to poll the property value -> raise data change event in the timer-> trigger subscription -> execute sync service to update the property value    ==> works 

Any idea about it ?  

Thingworx: 8.5.4

Kepware:  KEPServerEX 6.8

PLC: SIEMENS 1200

Regards,

Sean