Introduced with Jersey 2.31 the client connection timeout is the double of the configured when posting an entity.
client.property(ClientProperties.CONNECT_TIMEOUT, 2000);
...
invocationBuilder.post(null); // correct connection timeout of 2 secs
invocationBuilder.post(Entity.json(request)); // double connection timeout of 4 secs
Small Spring Boot example project here: https://github.com/oleborup/jersey-client-connection-timeout
To reproduce