This is the error from the nsclient log;
2021-01-13 23:14:19: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 11:19:50: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 11:20:30: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 11:22:33: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 11:23:07: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 11:25:03: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 11:25:37: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 11:35:33: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 11:36:07: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 11:45:33: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 11:46:07: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 11:55:33: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 11:56:07: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 12:05:33: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 12:06:07: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
2021-01-14 12:15:32: error:c:\source\master\include\socket/connection.hpp:139: Socket was unexpectedly closed trying to send data (possibly check your timeout settings)
These errors are flapping and it results the below alert in nagios -
CHECK_NRPE: Received 0 bytes from daemon. Check the remote server logs for error messages.