Sorry, I just found this thread and I'm a bit noob at this. I've been getting the same error as the OP. I followed this guide
https://3ds.guide/get-started for my O3Ds (a9lh and Luma CFW on 11.2). I restore the NAND.bin following the instructions from the reddit thread you've linked but I ended up staying on Sys 11.2 firmware with all my .CIA's gone (including FBI and HBlauncher). I believed restoring the NAND backup sort of worked as I still have access to my owned games from the Eshop but I've lost pretty much everything else beyond that from there (Though, everything I had still shows up in the SD card management in system settings). Is there any way of restoring these? As I am unsure of how to restore my old .CIA's including FBI and HBlauncher.