Client reports broken Post Preview function

I can’t duplicate the issue on my end and I can’t test on his (I’m in the US, he’s in the UK). He says that when he clicks the “preview” button while editing a post, instead of a tab/page opening and showing a preview of the post, he’s taken to the “All Posts” Dashboard page. I mentioned to him that once you’ve previewed, if you leave the preview tab open and then click preview again, the same tab reloads with the new preview, thinking that perhaps he was just looking at the wrong tab, but he doesn’t think that’s it. I’m thinking maybe it could be a redirect issue or a pop-up blocker or something installed on his computer and not on mine. I figured I’d check here and see if anyone else has experienced this issue. Previewing works completely as expected for me.