Varnish failing to detect valid probe page

[Victor.Grazi at nomura.com]

I am having a problem with Varnish 3.x probe page from a SpringBoot application (1.4). Varnish is failing to detect the probe page (returns 503 SERVICE NOT AVAILABLE) and consequently fails to route.
When I manually ping the probe URL, it works fine, but Varnish is flagging the probe page as being down.
Removing the probe page, everything works fine.
Pointing to a static probe page (my.css) or any other static or dynamic URL fails.
Looking at the logs, the response header looks like this:
HTTP/1.1 200
Content-Type: text/plain;charset=utf-8
Content-Length: 72
Date: Wed, 01 Feb 2017 15:20:48 GMT
Proxy-Connection: Keep-Alive
Connection: Keep-Alive

Comparing this to other working (non Spring Boot) applications, the only difference is that the working applications have an OK after the response, and the bad ones don't: HTTP/1.1 200 OK Does that mean anything?
For example, here is a good one:
HTTP/1.1 200 OK
Date: Wed, 01 Feb 2017 14:04:18 GMT
Last-Modified: Fri, 11 Nov 2016 22:00:02 GMT
Content-Type: text/css
Content-Length: 129
Server: Jetty(9.3.z-SNAPSHOT)
Proxy-Connection: Keep-Alive
Connection: Keep-Alive

Not sure where else to look! Any clues?

Victor Grazi

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