I’m curious if its only when you use the previous and next block that you are getting the wrong pages? I recently ran into that issue and had to make sure “exclude from nav” wasn’t turned on for the sub-pages, and instead turn on “exclude sub-pages from nav” on the top list page.
Or are you clicking a link for one page and landing on another? I found an issue like that when I deleted a page and tried to use the same url slug. I had to find it in the trash and remove the duplicate url.
If you are in the sitemap and click on a page and then click visit, does that always take you to the correct page?