Ground is missing at the output terminals, remove the back cover and inspect the soldering, it may be broken, resolder them and it will be working normal again, if the connections are ok, is possible that the output driver may be broken , in this case you will have to replace the output integrated circuit. That is not a setting problem, is a hardware problem.
You're right: there is no grounding at the output. Because of the particular design, I can't inspect the terminal connections without breaking the plastic housing to determine if resoldering would fix it, or if it's a driver issue. Thanks for the research.