Ben Sibley on "Tracks Pro background texture thumbnails not showing"

The background thumbnails in the customize menu are not showing. They still work if I click where a thumbnail should be. Screenshot:
http://modemotomag.com/wp-content/uploads/2016/06/tracks-pro-textures.jpg

This sounds like it could be a conflict with another plugin on the site.

Could you try deactivating all plugins on the site besides Tracks Pro? In the Plugins page, there is a bulk actions option you can use to quickly select and deactivate/reactivate all plugins.

Deactivating them won't have any effect on their current settings.