Getting some NL-Network-03 and NL-Network-01 errors during load test

I was conducting a load test for set of API calls and got a very small amount of network errors during the test. Although the number was insignificant what do the errors mean?

The errors are got are:

NL-NETWORK-03
java.net.ConnectionException: Connection refused: no further information

NL-NETWORK-01
java.io.IOException: Connection closed during ALPN negotiation.