Published pages suddenly not showing up

We recently updated to version 4.0, and now some our published pages have disappeared. I can see them just fine on the back end. All the content is present and the posts are set to published and public. They show up in the dropdown nav. But when you click the link in the dropdown nav, you get a “page not found.” Here are two of the pages in question:

https://sunnysidecsa.com/Vegetable-Fruit-Shares
https://sunnysidecsa.com/how-to-sign-up-to-volunteer

There may be more but I haven’t checked all the links yet. Wanted to see if there was a fix for this before I spent any more time looking at dead pages.

We have done nothing to change any of these posts. They previously worked just fine. I can see nothing weird in the page editor. Everything appears normal.

Thanks.