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Plant stress is a common cause of bitterness. Too much water or high heat are common culprits. Once the fruit begind to turn bitter, there's not much you can do. Future fruit will also be bitter. The season is still young and you have time to plants new ones.

You may have a pollination issue. Squash and cucumbers are pollinated in the same way, so these articles will help you:
https://www.gardeningknowhow.com/edible/vegetables/cucumber/deformed-cucumbers.htm
https://www.gardeningknowhow.com/garden-how-to/beneficial/insect-pollination-process.htm
https://www.gardeningknowhow.com/edible/vegetables/squash/pollinate-squash-by-hand.htm

This is caused by a pollination problem. You may need to hand pollinate if pollinators are having problems getting to your plants. This can be done swirling a small paintbrush inside a male flower and then swirling the brush inside a female flower. These articles will help with attracting more pollinators to your yard:
https://www.gardeningknowhow.com/garden-how-to/beneficial/insect-pollination-process.htm

https://www.gardeningknowhow.com/garden-how-to/beneficial/creating-a-pollinator-garden.htm

Gummy stem blight commonly affects cucumbers, as well as many other crops. Gummy stem blight can appear anytime during the season, but most damage occurs late in the season after the fruit is set. Warm, wet conditions favor the development and spread of the disease.

This fungus can be controlled with fungicides if caught early enough. To prevent re-occurrence, you should practice crop rotation. Do not plant the cukes in the same location. Also make sure that all plant debris from affected plants is removed and destroyed.

You may want to toss them. If they are large, then they are probably over mature. I would try picking them a little earlier. Some varieties may look white instead of yellow when over mature. Here is an article on when to pick cucumbers: https://www.gardeningknowhow.com/edible/vegetables/cucumber/when-to-pick-a-cucumber-how-to-prevent-yellow-cucumbers.htm

This article may also help: https://www.gardeningknowhow.com/edible/vegetables/cucumber/what-causes-bitter-cucumber.htm

Early on, squash plants will produce more male blossoms than female blossoms and, as male blossoms do not produce fruit, they often fall off. As the season progesses, you will get more female blossoms and more fruit. Here is an article with more information: https://www.gardeningknowhow.com/edible/vegetables/squash/squash-blossoms-falling-off-vine.htm