It sounds like it is an issue with the transducer on the bottom of your boat. Typically, we’d recommend hooking up a new transducer and testing it by holding it in the water with the cable connected to the device (i.e. don’t do all the mounting work until the old one is proved faulty). If the new one works, replace the transducer. If this is confusing we can come help you do this test.
If it’s not the transducer, it’s likely an issue with the chartplotter itself. The most we can do is a software update at our repair centre. Unfortunately these units are out of production and no longer serviced, so any problems internal to the chartplotter cannot be repaired.