Same issue here. I just got a well-used OneWheel+ with the rattling ferrite ring and only intermittently functional front LEDs. I suspect that the board took a hit in its previous life that caused the unsecured ferrite ring to yank the cable and partially unseat the connector to the LED strip. I disassembled the board and was able to reseat the connector with the front of the controller box pried open. That seems to have restored front LED function, and I'll plan to go back and insert some foam to stop the rattle and prevent further LED issues in the future.
Does anyone know how to safely and reversibly open the controller box fully?