You are using a preloader, and it works on the root site but does not work on a subsite.
The Publishing Feature on your subsite is not activated.
To make the preloader work on the subsite, you need to activate the Publishing Feature.
Step 1. Open the Site Settings
From any page within the subsite, click the cog wheel icon and then choose Site settings.
Step 2. Open Manage Site Features
You can find Manage Site Features option under the Site Actions category:
Step 3. Activate SharePoint Server Publishing
Scroll down to find Share Point Server Publishing option. Click Activate button:
This will enable the preloader settings on your subsite.