Bug one: Install the sbsbpa on the server and leave it as the defaults and it will throw off errors on every single client. Remove it, all is well. Workaround for now is to only install the BPA on an Essentials box when you need to run a scan, remove it for now.
Bug two: If you have archived computer backups but have removed the computers the UR2 update tries to do an inventory of the network looking for Mac clients to update. Because these past workstations are in the device XML listing, the inventory process will cause an alert every 1/2 hour to go off.
In 30 minutes that will be green again. Another 30 minutes more and it will be back to yellow.
If you are seeing this and your network does NOT have any archived backups in the console, please email me at susan-at-msmvps.com as I want to talk with you as to exactly what you are seeing in SBS Essentials.
Both bugs above are being worked on and there will be future fix. Stay tuned.