My 2015 Siesta has an Axxera radio which did the same thing. I disconnected the ground cable by the "gas" pedal, put the house batteries to store, connected the ground wire, and turned on the house batteries and that seemed to fix it. All the settings were gone though. Hasn't happened again. I believe there is a 15A fuse behind the radio, the trick is to get it out of the dash....
Steve
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