The UX of the dashboard and all plugin is "broken"

Hi, I've just installed the WPMU Dev Dashboard on a new web-site. Everything goes well until I wanted to install some plugins.

I don't know why, but the UX is completly different compare to the one in the others websites, and I can't upload plugin from the dashboard, or upgrade the one that are in free version in the WPStore.

However, even if I want to display every plugins available, it say that no plugin were find. I can't figure out why this happen, only on this website. And I cannot use the "Update everything" or "Install" from the hub, each time the process fail.

You can check this on these two screenshots :