Thanks for the support! Actually, I also suspected it could be one of the caching mechanism we are using… W3 Total Cache, CloudFlare CDN/ Security, and Hide My WordPress which is a security plugin that changes the path of all files and folders to custom names, but also minifies website files. So before contacting you…
1- We turned off W3 Total Cache plugin 'minify”
2- We turned off Cloudflare “Rocket Loader”
3- We turned off all plugins, but didn't try to reactivate them one by one because I thought the problem really might be with the caching plugins and CDN.
So with your suggestions, let me try adding “Related Post Pro” to the exclusion list of “Hide My WordPress” to exclude it from custom path, and check all other plugins and see what I can find and get back with you.
Thanks so much!