Maybe the cucumbers were overripe? I know it sounds mad, but our zucchinis are quite small when they're ripe and if i leave them longer than that they go soft from the end. Is it all of them or just some? If its sun, you could put a bit of cardboard over or some shadecloth draped over. Don't know how they are growing but something like that should help - we did that for our tomatoes which were getting sunspots. If its fungus, try neem oil.
our garden is a bit wild at the moment. The punkin vine has taken over in one bed and the other one hasn't been replanted yet, has some nice herbs growing though. It just got so dry here and hot that I spent all day bucketing water from various places and ran out of time to garden. It has been raining a bit this week so maybe this weekend I'll get back into it. Love picking the veg, its the best!