Looks like leaf miner to me. Practically all my plants are affected by it.. I've just been mostly ignoring it. It's not out of hand or anything.

Mine ended up looking like that. I didn't know what happened w/ mine, either. I am getting a couple of new vines out right now. I don't know where you live but I live in scPA and we had a lot of heat waves this summer -- maybe more than any summer. Probably the vines were just stressed out by the terrible heat. I'm thinking I might try some new cukes myself! I heard that most veggies really love the rains w/ the tstorms! We weren't getting that many tstorms lately, just some rains about once a week. Don't know what your pest would be.