I have raised a ticket with the host to update to 7.3.13 on the basis of security patching - would that version be enough to fix the problems?
I'd guess that you have a very rare problem: your server doesn't provide the info needed by the .htaccess file and you need to replace your current .htaccess: https://open.vanillaforums.com/discussion/comment/259810/#Comment_259810
Super, I was just checking at this very moment
I noticed that Keystone theme is not active for mobile on your site
Just checked and there are currently no Theme fields in config.php
You can set the mobile theme in the dashboard