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The only thing I can think of is a fungal or bacterial leaf spot problem, most likely from water on the leaves. Humid conditions, overcrowding, and poor circulation can also contribute to leaf spot. Remove and destroy all the affected foliage. All leaf spot diseases can be controlled by decreasing or eliminating overhead irrigation, minimizing leaf wetness periods, discarding heavily infested plants, and applying preventive fungicide applications.

You could try it, though I am not sure how well they will turn out. If they are already bitter tasting, this may not be improved with the pickling process. Here is an article that you may find helpful for future reference with bitter cukes: https://www.gardeningknowhow.com/edible/vegetables/cucumber/what-causes-bitter-cucumber.htm

Cucumbers and squash are in the curcubit family, but they cannot cross pollinate. It is like humans and monkeys. Same basic family, but not compatible. Here is an article from the Iowa Extension Service on why it can't happen: https://www.ipm.iastate.edu/ipm/hortnews/node/981

There are cucumbers that look as you describe. You may have a mislabled plant or seed in your garden that was mislabled by the company that sold it to you.

This article should help: https://www.gardeningknowhow.com/edible/vegetables/cucumber/what-causes-bitter-cucumber.htm

This article should help with that: https://www.gardeningknowhow.com/garden-how-to/seeds/what-is-damping-off.htm

If any of the others look the same, snap a picture and send it in. We can better determine what you have or what is going on this way.