Subscription between SCADA (OPC-UA Client in C#) and OPC-UA Server (OPC-UA Server in C) is lost|OPC UA Implementation: Stacks, Tools, and Samples|Forum|OPC Foundation

I have been assigned SCADA SW where a C# Windows 7 based application communicate with OPC-UA server (in C Embedded Linux environment). SCADA subscribed number of events/Data value changes from the OPC Server. We are showing some server data in UI. Most time it works fine but sometimes the UI is not updated. I have tried to reproduce it in my office environment with same SCADA and same OPC-UA server. I never see the problem.  But in field, I see we have many times (not regularly or I couldn't follow or find a pattern when it happens) it happens, the UI is not updated though there is connection between SCADA and the OPC-UA server. If I restart the SCADA then it goes away. I guess it is related to subscription? What I am missing here?

Anybody else has similar problem?

Thank you.

Mahbub