Blight/sunburn or windburn

Hi 

I have started growing butternut squash for the first time.

i currently have some in the window upstairs and some In the lean on 

i have recently noticed a couple of the leaves deteriorating, at some point I had the Windows open upstairs to let air in but I am not sure if this began before or after that.

i have cut some leaves off but would like to know what is happening incase there is something else I need to do.

a similar problem happened when I grew courgette for the first time last year, the plants were in the ground and the leaves went grey and wilted then died but p strangely the plants came back and I was able to have three courgettes befor the frosts set in.

Also pictured are tomato leaves which are near the butternut squash

thank you for your time!