Hello! As stated by Kelsee above I would agree the browned part of the cucumber looks like sunscald.
The other photo of the stem definitely looks like squash bug larvae has attacked your plant's stem. They lay their eggs which are copper/red colored on the stem and once hatched they burrow into the stem and eat it from the inside out.
And look in the 'Squash Bug' section farther down.
Or this is one of the many YouTube videos out there related to this issue:
I have treated the bugs and their eggs on plant with a 8-insect pesticide (mainly on stem) and the eggs have died off without infecting the stem.
Otherwise some of the leaves you have shown look like mineral deficiency (or overuse as suggested above). Those vids also include tips on proper fertilization of these plants as well. I have tried that and have stopped the squash borer and the leaves are looking heathy so far too.
Hope this helps!