Thanks for the question.

The yellowing/brown leaves are most likely a watering problem.  Too much or to little can show similar results.  Some of the green leaves seem to show some yellow spots developing.  Flip the leaf over and you may may see white spots of powdery mildew starting.  Potassium bicarbonate works well for this. Grayish purple fuzz may indicate downy mildew which will basically end your cucumber season. Dense groupings of flowers can indicate plant stress from the weather or disease; however, this looks normal.  Check out the following links:

https://extension.umn.edu/diseases/downy-mildew-cucurbits

https://extension.umn.edu/diseases/powdery-mildew-cucurbits

I hope this helps.