Are you per chance using an external screen? At least on our S5000, the console will come up (either turning it on or loading a show file), then IIRC the faders will start working while the UI (screens and softkeys) resets itself to get the external screen going.
Maybe if you are using an external screen, the cable has come loose or is failing.
We’re using firmware 1.96, but the behavior’s been more or less the same since we got them (before 1.9 came out).