Hey, i’ve not used my slim phatty for a couple of months, switched it on tonight and the first key responds when you hit it but the second key takes like 3-4 goes before a sound is played…
is this a faulty keyboard?
Hi!
Where is the first key on your Slim Phatty? 
Joke aside, check the PolyChain setting in the menu. I guess it is set to “1 of 3” or “1 of 4”.