GPS Question/issue

I'm having a problem with my handheld Lowrance Ifinder GPS. I have the Fishing Hot Spots map installed. Some of the lakes I fish, it will show that my boat is actually on the bank when I'm 40 yards away from it. It's kind of like the map is out of sync with the actual coordinates. The current GPS location coordinates are correct. I also have a gps/sonar combo by Lowrance and this unit shows the exact same coordinates as my handheld but it shows my boat where it should be.

Anyone have any ideas? I've e-mailed Lowrance but no response back from their support.

Thanks

I would guess that the lake is at a higher water level than the map depicts. All maps of lakes are at a certain lake level. These maps don't change when water levels go up or down. It has been a very wet year.