WordPress 4.0 Menu not saving additions, removed menu from theme locations

Everything worked fine prior to the WordPress 4.0 update.
Now when I add a Menu Item (page, link, etc) and click save, it removes what I added and removes the checkmarks for the “Theme locations” under the “Menue Settings”.

Here’s a video showing the issue: https://screencast.com/t/teAGzWY25You