This can happen with some varieties of corn on the cob. In my experience, some types are better than others. I have found that Silver Queen and other SE varieties of corn tend to have softer kernels. However, the kernels of the super sweets are that much firmer and stand up better to freezing. Remember not to over-blanch them. This can be a problem too. Keep to the times I’ve recommended above and cool in the iced water straight after blanching. Be careful not to overcook the corn when blanching, too! Stick to the recommended times and get the corn into ice water right afterward. When you later come to reheat the corn, transfer it from the freezer into the boiling water directly. You’ll need to cook it through for approximately five minutes to ensure it’s heated through properly. Be careful not to overcook, or you’re going to get mush again.