Does this only happen in shallow water (you mentioned 10 feet)?
If so, than a software update may help.
If not, than you may have damaged the transducer, transducer cable or the transducer. The problem could also be internal in the unit itself. See if there is someone that you know that is running a Humminbird unit and would allow you to test your 365i on their boat to see if the problem is in your unit or transducer. This does not have to be another 365i unit as most use the same 200/83kHz sonar (even the Si units).