Gentlemen,
Thank you for your suggestions- it fixed my problem.
For future reference and to help others, what I meant when I said some pages don’t load was this: an error message that said something like ‘the URL siteA/page1 could not be found. No error number as far I remember- I fixed the issue before noting down the exact wording!
I went into wp-admin as suggested and changed the permalink structure from post-name to default. This seemed to fix one of the problematic pages but not the other two. I then changed it back to post name and that fixed all the pages.
stoatoffear, I’m not savvy enough to follow your suggestion of changing string length, although I didn’t need to do it to fix my issue. Someone else might find it helpful.
Thanks for the help again.