K12 automatic juddering

I have a k12 Nissan Micra automatic, and just recently I am getting a juddering (like it can't find the gear) when in low gears and accelerating up. It seems completely random as does not happen all the time I fact just 3 times in a month. The engine Sounds fine and the revs go up and down quick and then it finds the gears and then works ok again.
Any help much appreciated.
 
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