A127 losing bottom?

[Whatadeal]

Having problems with my a127. No particular pattern or reasoning but it happens 2-3 times during a trip. I fish for salmon and run downriggers. I will be in 100 plus feet of water and all of a sudden the depth with start reading the cannonball depth (lets just go with 40 feet).
It has also done this when coming across a large pod of baitfish.

Sometimes it will start reading normal again on its own, other times I have to go to the main fishfinder screen and adjust the gain all the way to zero and wait about 30 seconds and it will start reading correctly.

I updated the unit about 30 days ago, did it before then also.