Older Entries Link Jumps Back 10 Pages

I have a friend who runs a blog but is not familiar with the technical ends of it all so I help manage it for him.

Recently he’s been having an issue with his Older Entries link. Whenever someone clicks it, it takes them back 10 pages. This is a problem that doesn’t happen to all his readers though. I’ve tried several times but the Older Entries link works fine for me. It wasn’t working for him either but after a while it was back to normal him. He’s still receiving complaints about it from his readers though.

This is the blog: https://www.theprophetblog.net/

I can’t seem to figure out the problem. Any help we can get would be most appreciated!

Oh and I think I should mention that some time ago he was using an ad program called Yashi but removed it because the ads started showing porn. He’s wondering if perhaps it left a virus on his site (my anti virus doesn’t seem to pick up anything though.)