This error with a disappearing context menu was driving us crazy. Whenever we tried to open a menu in the ribbon, it would close as soon as we opened it.
Luckily we found the culprit in the form of the Dropbox “Badge” add-in. Simple rightclick your dropbox icon and chose “Settings” then under “General” under “Dropbox Badge” select “Show never”.
Afterwards our context menus in the ribbon were back to normal!