The last couple of weeks I have a similar experience with a single circle, except for the fact that it is not switching on/off all the time, it just switches off and stays off.
After plugging it into a power socket it switches on. Then, after 2-4 minutes it switches off and stays off. Also the status in Source is changing from on to off. After that I cannot change the status to on anymore using the software. When I unplug it and plug it back into the power socket everything repeats itself.
I noticed it because it was on a schedule, on during the daytime, off during the night. Suddenly it just stayed off.
Have to check to make sure, but it probably is too old (>2 years) for warranty.
The money I saved by saving energy is now well compensated by the cost of the circle and possibly a replacement circle. Not sure if I will replace it.