If the dashboard for your Google+ Page is showing that you suddenly have zero followers, two things:
1.) You’re not alone.
2.) Google knows about the problem and is working on a fix.
I started noticing the bug yesterday: All Google+ Pages that I manage are showing that they have zero followers. It’s happening only on the main Dashboard page for all of my Pages (plus.google.com/dashboard), as well as the dashboard pages for each individual Page. The Pages themselves show the correct follower number, so users aren’t seeing the bug, only Page owners see it in the dashboard view.
Here’s how it looks for our Marketing Land and Search Engine Land pages.