It sounds like you're covering all the bases, especially by growing some pollinator-attracting plants in the yard, though weather might be playing a role. High summer heat and other environmental factors can promote the formation of male flowers over female flowers in cucumbers and other vegetables. High heat can also kill pollen, so even if male and female flowers are present simultaneously, the male flowers might be rendered infertile. Granted, we don't have excessively high heat all summer continuously, but if any sources of reflected heat (a nearby wall, plastic mulch, a stone pathway, etc.) happen to be near the plants, that might be contributing to heat buildup or overnight temperature levels remaining higher than the plants prefer.

If you do see male and female flowers open at the same time, you can definitely try hand pollination. Guidance can be found in the page (and its included links): Pollination of Vegetable Crops in a Changing Climate. In a future year, perhaps experimenting with a parthenocarpic variety will ensure more reliable fruiting since those types don't require pollination to set fruit.

Miri

Thank you. This is fascinating information. 

Thank you Deborah, and it's no bother -- this is what we're here for.

You might be thinking of the Master Gardener program; it has a volunteer requirement component, but there is a relatively new alternative (but with much more limited capacity at present) to learn similar information with no volunteer time required, which is the Sustainable Horticulture Certificate. It was only developed recently, and might be refined as we receive feedback and make updates to the content as needed. There would be a lot of overlap in the content presented between those two options.

Generally, what affects cucumbers can affect summer and winter squash, as they are all cucurbit family crops, so yes, high temperatures might kill pollen or trigger flower sex ratio changes in both plants.

Miri