Cannot go back a page in Safari

Hi! I haven't done one of these before, so hope it works - any help appreciated! When Voiceover is running on my MacBook Air, I used to use the VO keys and the back and forwards arrows to go back a page or forwards a page on websites but this seems to have stopped working. I emailed Apple and they thought it could be a problem with my Mac, but I've tried to replicate the problem on another Mac (that is used by a fully sighted person so has no preset accessibility settings) and come up against the same problem. Any tips or advice please? Thanks!