I'd try another unit first just to make sure your puck isn't messed up.
You know you can't be going at more than wake speed, right? Other than taking depth off auto, I change the default on scanned distance out on either side - SI Range (not sure if that is still a config setting on the newer models). Also try setting the sensitivity level in view mode to highest setting - mine is 20 I think and even go to showing just one side so you can focus on how you are tweaking it - SI Side selection. You should experiment with color to show the shadows and details you want while you are fooling around.
The last thing I would do is increase the chart speed so it collects and paints more info on the display - I know it is counter-intuitive but that's how it works at least on mine.
One other note - I got so twisted in making changes that I couldn't get it to show anything I thought was there and selected default and started again. From time-to-time, I select default and then re-enter what I think is right for the water I am fishing.
If you have split-view, stick with just the SI view for now and as you see more details, switch to split view and show down imaging or regular sonar on the other view to see how it syncs with what you are seeing on the SI view.
Not sure if that will help you but that's what I do. I have had my Humminbird units now for many many years now and enjoy them. Bill, the MadKayaker