Good day, for some reason when a user loads our site on a mobile phone the following error is shown:

"Cannot Create a _mobile_failover_mode.htm" file. File permissions for the . directory have not been set correctly.

This is odd, as the Auto Upgrade function works correctly, and I even ran the "fix permissions" ..  

Hello,

It sounds like you've enabled failover mode in the config editor (config_editor.php, "Installation options").

I don't know the exact cause of the error off-hand. But if you disable failover mode that should go away.

Hello again,

I've had a closer look.

There is a bug here, and it occurs under the following combination of conditions:

1. Failover mode configured (as mentioned in my prior post). This isn't a default, so you would have enabled it.
2. User on a mobile device.
3. Guest user.
4. Static cache configured.
5. Non-suEXEC server

The issue is fixed in this sources/site.php:
https://raw.githubusercontent.com/ocproducts/composr/master/sources/site.php