| if i knew that i would be a very rich man!
my guess...
When sensors, electrical connections etc, work ok when you're out riding then not work the next time it fires up. my theory is that heat cycles have something to do with it, runs fine when hot and clearances are different, particularly things like sensors on the motor that get very hot. then when things cool down it triggers the failure/connection break etc.
These things often start with an 'intermitant' fault then totally go, but you may not notice your rev counter packing up for a second or two when your riding, easy to miss. | 
wilf
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