I too am having the same problem of losing sonar. I've been in contact with Lowrance and will post the outcome. LCX-15 mt Mine did the same thing in January, I ended up sending it back. At the time it was the first one returned. I have not had the problem since.
Unit works great.
Three Rivers is the place to get one. My unit has the GPS module but does not have the mapping accessories package. Sure would like to know more about the cause and how widespread the problem really is. I couldn't be any happier. You have to understand that I had a basic eagle until I got the lowrance.