We have a peculiar situation where an XMLFW will only process when a probe is turned on. When we turn the probe off, it is as if the service isn't there.
I came across some others having similar problems, but we're not doing a pass-through, not piping the processing through.
It is a JSON in / JSON out service with a static back end, and we allow processing with an empty message body. There's really nothing super-fancy going on.
There are 2 request rules and one response rule. One request rule looks for a login request and applies a very basic transform on the message body. All other requests go through a second rule that really does nothing. The response rule also does no real processing on the message ( meaning I could have JSON/Passthrough, but I don't).