I am plugged directly into the wall outlet and have tried multiple outlets in 2 different residences in Chicago, Illinois and Orlando, Florida. The issue seems to come from stress on the solder joints on the circuit board. Careful positioning of the power cord on my fixture seems to correct the issue. This has happened since I got the fixture in August. Not really a big deal since once I get the fixture set up and the power cord set up with little tension on the point where it goes into the fixture, that's where it stays and the lights don't flicker when positioned in such a way.
When I get a chance, I want to open the fixture up and re-do the solder joints to see if that corrects the problem permanently. I've been wanting to open it up anyways because I want to have an independent power supply for the "moonlights" so that I put them and the daylight bulbs on independent timers to automate the fixture.