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Canon EOS series cameras (including popular models like the 5D Mark IV, 6D Mark II, 90D, R5, R6, and the 1D X Mark III) rely on a sophisticated internal system known as the EFI (Electronic File System) . This system manages everything from lens communication to image processing. Over time, users may encounter firmware glitches, boot loops, or "Lens Communication" errors —symptoms often resolved by performing a complete EFI software reset .