Just added some new panels to a small system running at home based on a Multiplus-II with a Smartsolar MPPT controller and the ESS assistant running. It's all been running fine with no errors...until I shut off the solar panel power feed to the MPPT to wire in the new panels.
Apparently, there is something in the ESS/Multiplus-II/Smartsolar that causes the Low Battery LED on the Multiplus to start flashing when the solar power is abruptly cut. I got out a meter and checked the actual voltage at the Multiplus input and it was a very stable 13.18 volts -- definitely not low. Bypassing and powering down the Multiplus extinguished the flashing light. There was no entry in the Notifications log for the ESS of anything being wrong.
I duplicated the error again today but was able to recover by just completely removing the load from the Multiplus for a few seconds. Not a significant problem, but it does give quite the start after weeks of good performance only to see a flashing red LED on the most expensive piece of the kit.