G500 going 'limp'

Guys,

The most frustrating thing occurred tonight.  A fellow gwoa member was test driving my G500 when it went 'limp', not once, twice or even three times but 4 times in quick succession.  I have covered some 14000 miles and not had this problem:

When going through the gears 'manually' ie selecting 1,2,3,4 as opposed to having it in D there was near total power loss, you could put your foot to the floor and nothing would happen.  Power would slowly come in but way down on what it should be.  'No Malfunction' was displayed on the command screen when these symptoms were taking place.  Switching the engine off and back on again instantly resolved the issue.  The G was being driven by manually selecting the gear for pretty much the first time in my ownership and was being driven far more aggressively than normal.  Following the fourth shut down a 20 mile drive then a 40 mile drive were completed with absolutely no sign of an issue, kicking down when it should changing gear when it should etc.

Needless to say there has been a lot of head scratching.  Anyone experienced this, or have any idea what the problem might be?

I put it down to it not wanting to leave me...

Thanks,

Ian