I had the exact same problem.
Solution: unplug the charger from the wall for a few hours (minutes “might” be enough)
More details: Despite the green light on the charger, I used a multimeter to test the barrel plug that goes into the robot, and to my surprise there was no DC current going to it. I tried to unplug the charger from the wall for around 10 seconds and try again with no results. So, I unplugged everything overnight (and day as I went to work). I plugged everything back in today, and to my surprise the robot started charging again.
My charger is on a covered patio away from any moisture, but we had some extremely hard rain the night before I had the symptoms you did which led me to think that maybe some moisture got in. However, the charger still stayed green which was very deceiving.