I'm the other poster that intheswamp mentioned. Having very similar issues. Unfortunately it's hard to identify.
I updated my profile to show I'm in zone 6b. Kansas. Are your plants Bonnie transplants or did you start from seed?
It seems like it could be fusarium rot, damping off showing up late or possibly bacterial wilt spread by cucumber beetles. I have seen a couple spotted cucumber beetles on a more healthy Armenian cucumber plant. These beetles can feed on stems and roots below the soil and they can spread bacterial wilt.
Here's 2 more plants that died off and wilted completely yesterday. You can see the shriveled and wood like stem damage that is occurring in this bed below the soil.
Sigh.
Thankfully a few of my cucumber plants in other beds are getting bigger and look like they might make it
