Squash vines in distress

We went to the allotment today for the first time in about a week, and some of the squash vines are looking pretty poorly. We've had a few cases of apparently fertilized fruit rotting, which sounds like it's quite common this year, but these vines look pretty bad and were a bit of a surprise. And advice as to what might be ailing them would be gratefully appreciated.

Things I've done which may or may not have something to do with it:
1) about a month ago, i move some of the vines in order to clear out a lot of weeds which were growing about the squash bed
2) 10 days ago, I fed them all with comfrey soup. This has been applied to all the squash plants, some of which are not suffering, and the french and runner beans, which are also fairly happy
3) also 10 days ago, mulched some of the squash bed with comfrey leaves/grass cuttings
4) sometime in the last few weeks, i pinched out the tips of some of the vines
I can't think of anything else out of the ordinary I've done.

Here's a picture which is not that clear, but there are three plants in the bed - the bottom one is in a really bad state, the middle one (courgette) is fine, and the top one is doing ok if not great:

Thanks for the reply.

Looking at last year, it seems as though we got quite a bit more growth from our squash in September, but this year the progress to date has been less good than last year, and the prospects for a long hot autumn seem dicey.

I guess you cant have success with everything.