It’s definitely the room lights. If I turn them off and only use the LED tube inside the frame, the image is solid. Turn room lights on, flashing noticeably.
I guess there’s some ripple in the LEDs’ power supply? They’re drop ceiling troffers refitted with LED “tubes”, kind of a big thing to replace and then, which tube is actually going to show up stable on the camera without buying each one and trying them to find out?
Circuits aren’t going to matter. The lights have some 60Hz flicker, all that could do is shift the phase +/- 120 deg. The camera’s power cannot be a source of flicker in its imager.