Some old posts are now missing?

I can’t pinpoint exactly when this happened, but at least a couple of posts on one of my wordpress sites have now disappeared. The address brings up everything except the post content, and since the site has been around a while, I wouldn’t have noticed unless a visitor had commented on the blank page they found. To illustrate, here is a normal page on my site:

https://www.shredaholic.com/how-to-create-great-guitar-solos.html

and here are two pages I’ve found that are no longer displaying their content:

https://www.shredaholic.com/campeselesson1.html
https://www.shredaholic.com/user24.html

if I go into editor, the post content is all there and it looks normal. Updating doesn’t bring it back, nor does drafting or trashing then bringing back to published. I’ve had to temporarily repost the content in the comments area for our visitors.

I’ve so many posts on this site (well over 300) it’d take me a long time to check them all for this problem. What’s going on here? Any help much appreciated!