I recently found that I am suffering with this problem as well.
I am in a similar position. WP SEO by Yoast ceased to function on my personal site as well as several or my clients sites. I sent a mail to yoast support and they informed me that they will only help me after i purchased the premium version. I have also found several other threads outlining the same problem and all of them eventually recommend using another theme or plugin… I do not wish to do either of these things.
I did try to switch to AIO SEO. Same problem (?). Switched back and it still didn’t work on those same pages. Tried to write a new page (worked) a new post (worked) and it also did work on some other posts.
I can’t seem to figure out why it doesn’t work on some though…
Zee
(@laserjobs)
Do you know the version of PHP?
What version of WordPress SEO by Yoast were you using before you updated?
Does it work if you reinstall that version?