You have any security plugin installed. Either disable it or exclude guest.vary.php for execution.
There are no security plugins installed currently.
The only security software being used is WordFence, but this is not yet activated.
No security plugin nothing will be blocked, so please verify if WordFence isn’t running. Also check any other functions that prevents running guest.vary.php. This file is safe.
I’ve now completed deleted WordFence, but the problem still exists and there are no other functions that would prevent guest.vary.php from running.
… and there are no other functions that would prevent guest.vary.php from running
Nothing happens without any reason. Normally guest.vary.php isn’t blocked by anything, so there is whatever that detects any malicious in this file. Please check your server/plugin configuration again.
Thanks again for your response, I’ve now resolved it.
In case anybody else has this same issue:
This was being caused by some .htaccess directory hardening rules that were put in place the Siteground Security plugin. The site isn’t on Siteground now, but was originally developed on there. So, when the site was migrated, these .htaccess rules also came across.
I’ve now removed them and all is well.
Rob