did you ever figure out what the problem was?

Possibly cucumber bacterial wilt, which is spread by cucumber beetles. Look for small yellow and black striped beetles in the early evening. The other way you can diagnose bacterial wilt it by breaking off a branch or stem and observing a white milky goo. Either way, you should dispose of the plants asap.

nice info!

Looks like some kind of insect ate your cucumber leaves. It might be cucumber beetles. Use treilis net so that your cucumber branches could spread and therefore produce more fruit. If your plant suffering bacterial wilt the trunk and the leaves should be brownish or yellowing. Your leaves are not wilting so it has to be caused by insects.