You are running a Carbon unit with an HDI Skimmer. Just installed it yesterday like a fool and lost downscan. Called Lowrance, on the phone for hours and they said the ducer was bad which I had a feeling was not. Reverted back to 18.3 and guess what? Correct, downscan is back.
This is the second time I can count where a software upgrade kills a transducer. It happened to the spotlight transducer not too long ago. This is just plain sad.