Hi Maxim,
This is what I could find in the error logs
2017/05/15 11:32:18 [notice] 21499#0: signal process started
2017/05/15 11:32:19 [alert] 22030#0: sendmsg() failed (88: Socket operation on non-socket)
2017/05/15 11:32:19 [alert] 22030#0: sendmsg() failed (32: Broken pipe)
2017/05/15 11:32:19 [alert] 22030#0: sendmsg() failed (88: Socket operation on non-socket)
2017/05/15 11:32:19 [alert] 22030#0: sendmsg() failed (32: Broken pipe)
2017/05/15 11:32:20 [alert] 22030#0: sendmsg() failed (88: Socket operation on non-socket)
2017/05/15 11:32:20 [alert] 22030#0: sendmsg() failed (32: Broken pipe)
2017/05/15 11:32:20 [alert] 22030#0: sendmsg() failed (88: Socket operation on non-socket)
2017/05/15 11:32:20 [alert] 22030#0: sendmsg() failed (32: Broken pipe)