Subscribers all switched to "no role for this site"

I'm running a two - site multisite setup.

A few days ago, all the users (subscribers) on my secondary site were suddenly switched to "no role for this site" under the edit profile page.

This is preventing them from editing their entries using the Formidable plugin, and also from editing their own profiles.

I've turned off all the plugins, and it had no effect. So, ideas, anyone?