Evidently the MoD don't have an issue with it or the callsigns/info would also be blocked for UK military aircraft. I am surprised the Shadow appeared on FR24 and suspect it was a training flight, but I'm more inclined to think that the particular device that allows it to be tracked is not in use when it is going about its normal business -as too would any aircraft the RAF doesn't want Tom Dick or Harry to know what it's doing. For example, I think it's unlikely Typhoons will be transmitting their location on a public website if launched on QRA or any other operational sortie.