when you say "squishy," i'm imagining the consistency of a warm marshmallow. that would be very unusual. they also should not "melt" in the sense that they become runny (unless you put them in an oven).
otherwise, some holds can become pliable under summer heat, but it depends on the composition of the PU. regardless of the company, the amount of hardener they put in the mixture isn't always exactly the same. if you contact the manufacturer or whoever you got the holds from, maybe you can get a refund or some replacements from a better batch of holds.
you can also ask on routesetters anonymous to get some other perspectives. i know this topic has come up a couple of times on there.