What do you mean by gaurdian mode? I'm having a simliar issue with my 2005 X-star with an MCX. Take it to the dealer and they said they cannot read the codes because they are soft codes and are deleted off the computer after 3 warm up and cool down cycles.
Dealer fixed what they thought was the issue and the next weekend we take the boat out and it throws check engine on the first set back! The boat looses power and sits in neutral flashing check engine with the engine running but no control with the throttle (is this what you mean by gaurdian mode?) We turn the boat off then on and it works fine.
I think my issue has something to do with my perfect pass as I only experience the check engine with perfect pass on. Looking at buying my own code reader to scan the code as soon as it happens out on the water to solve the problem once and for all.