The multisite theme manager no longers display the theme's images properly .. please see the attached screenshot. Notice how the customize button appears .. and on hover, the (activate) and (live preview) buttons appear over the theme image. I've tested that on a new multisite install as I was not sure which plugin cause this.. but now I'm sure it's the multisite theme manager. Once I deactivate the plugin, the themes appear normally. It works with WordPress 4.8 but not 4.9.