windows – TCP connections retains even sessions terminates

We have client/server application running in our environment, we are experiencing an issue that single client having multiple connections to the server, although, there is only one instance is running on the client machine.

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We have server running Windows 2016 standard and clients are running Windows 10.

On the other note even we are killing the process manually from Task manager and terminating the application despite connections being retained. We have tried clearing DNS cache and renewing IP as well as restarting both server and client still issue persists. Any help would be appreciated.