it might be a plastics problem in a certain batch it might be a location based problem caused by shipping....
some plastics don't travel well and if subjected to low or high temps or pressure changes (like say in an airplane) they will become brittle and prone to fracturing,
we don't know where the keys have been before the op got to use them, if for instance a courier chucked a pallet full of keyboards In the back of plane for a night flight it could induce such problems in the plastic of only those boxes on the outer edge of the pallet, this would give a high failure rate for a handful of keyboards but leave the rest with normal expected life, if a delivery company lobbed a pallet of pc parts into a freezer container to fill up space on a transit run it could induce problems in the parts... no fault of the manufacturer
if I was the op I would probably be talking to customer service to sort out getting the current keyboard replaced having that many keys fail isn't normal, having had my keyboard for almost a year and still not having any problems with the default keys it does seem odd that some folks with newer ones are having such problems