CP470 bottom tracking Issue

[cyberswede]

I've got an odd problem with my fish finder that I can't figure out, might just be a setting I'm missing or maybe something technically wrong it, tried everything I can think of. See attached picture. It was installed this spring and I'm still trying to figure out all the settings. While I'm offshore 1000+ ft and have the fish finder set to 300ft it occasionally moves up the bottom like a ran over something completely solid .. not even a initial mark or anything. I don't think it's a bait ball since it is just a perfect square. I have an Airmar A00013, 1kW Chirp transducer that is mounted on the transom. Not going fast either just 6kt. It does the same on the high Chirp channel as well. The MFD version is 17.45 and I believe the CP470 has the latest software in it as well. Anyone seen anything like this before?