I've had a similar problem with my LCX 27C. The software is up to date. Lowrance looked at the head unit.

The most consistent problem is that is starts flashing in depths over 40 feet and won't register anything. It rarely registers while on plane. Other times it starts flashing no matter what. Finally, sometimes it will register but with a mostly white screen...barely showing the bottom or structure.

Bought a new transducer over the offseason, hopefully that is the trick.

Does anyone else have any theories??