WPMU DEV dashboard disappearing intermittently

I am a super admin for my site and have the WPMU DEV dashboard installed at the network level. It seems to be disappearing intermittently. I have not yet found a clean sequence to reproduce.

When it disappears, the only way I have found to bring it back is to deactivate and reactivate the plugin. One clue is that when it disappears the "activation" state still appears active.