I have several units at a Customer site that are responding to HTTP posts to /ue/rci with "404 Not Found" when I am setting the GPIO bits. All have the same firmware and were tested at our factory at the same time. Four units perform normally and three units return the error code.
I thought the Customer was not allowing enough time for the units to boot up but I could not replicate the error with my units. (Not likely a likely problem but worth a try.)