My 11801 had that problem, but I came to the conclusion that the NVRAM contents can be regenerated via one of the menu options.
I am not about to swear that's true. The manual and the FW are so bad they make the cheapest Chinese DSO look good. But I spent a good bit of time on the topic. The conclusion I came to was that the NVRAM is used to store the results from the "Enhanced Calibration" menu operations if the scope is powered down.
At any rate, I *love* my 11801 even if it is the worst FW I've ever seen. I've got four SD-26 heads for it. And a 2nd unit in CA at my sister's for spares and awaiting shipping when she has time.
I'd be very interested in any information about any information stored in the NVRAM at the time of manufacture and how it is generated and stored.