I fixed this on client’s side by increasing timeout value before connection should be terminated.
configure VPN remote connection timeout:
- On the client computer, for connections created using the Network Connections Wizard (NCW) and for Connection Manager (CM) profiles, the idle timeout timer can be found in the connection properties:
- From Network Connections, right-click the RAS connection, and then select Properties.
- Go to the Options tab.
- For NCW connections, use the drop-down list to set the idle timeout timer. For CM profiles, use the drop-down list to set the idle timeout timer for the connection.
- On the server running NPS:
- In NPS, right-click the network policy for the client computer, click Properties, and then click the Constraints tab.
- Under Constraints, click Idle Timeout to display and configure the settings of the timer.