Had a slight problem after the database server had to make a unplanned reboot.
I have a Network running on the WordPress installation; the sites were working, the dashboard was working however I did not have the insert image icon in the posts and the Super Admin was not visible.
For me this turned out to be a simple. The database table “wp_sitemeta” was marked as crashed and could not be read by WordPress.
This is likely to be the problem if the Super Admin disappeared after a hard shutdown of the database server. (By hard I mean that the database didn’t have time to close tables, finish writing to tables etc)