Is your zuke cucumber mosaic virus (CMV) resistant? Splotchy light and dark green leaves can be caused by that.

I don't think mosaic would appear over night. Looks to me as if some creature has eaten off the outer layer of the leaf. I’d go out after dark with a flashlight and see if you can surprise whatever it is.

I would plant a few more seeds.

The zuc is black magic zuc is black beauty. I have never seen anything like this. Note the dark dots might be tiny bugs hard to tell. I have planted it before.

I found a slug this morning but damage does not look like slugs.

Does it look like actual physical damage, or does it just look like discoloration? Can't tell from the picture. If the former, it's bugs, if the latter, then it's likely disease.

Physical damage - good point. What is weird is it looks like a layer was eaten off - a VERY thin layer. I have never seen anything like it in my garden.

You were talking about sunscreen chemicals, is this a plant that could have gotten damaged by a chemical? If it grows a new set of healthy leaves it could be okay. If not, easy to replace with new seeds.

No this was definitely not a plant that got anywhere near sunscreen and I never touched it. A new one popped up and I am watching it closely. Really unique what happened I have seen a lot in my garden but nothing like this.

Might be teeny tiny baby snails or slugs. Some start out very small - like a grain of sand - and can do damage like that.