I have a Helix 5x Chirp Si GPS G2. I have installed an XNT 9 20 T  transducer for sonar reading. and have the supplied transducer mounted for Di Si. etc. Humminbird  notes that the XNT 9 20 T  is  a compatible transducer. I cannot gat a correct bottom lock on the unit when I choose "Auto" in the menu. I can set the depth manually and It seems to read properly but in auto mode it will display anywhere from 320 feet to the 1500 foot range. When it is reading at the 1100 foot range I can see a thin line on the very top that is probably a display of the 30 foot depth that I am in. In the manual it states that Fresh water is normally 0 - 330 Feet so I made sure it was set to fresh water. As some of the lakes I fish have varying depths its difficult to keep changing the depth range while I'm fishing. The last unit I had would automatically change to the nearest depth range to suit the depth I was fishing. The unit is 3 years old and I have 11 hours on it. I did not use the boat last year but I don't recall having this issue the year I purchased it. Its probably some setting that I ha checked off incorrectly but I cant locate any menus that don't have my settings correct.

I have the same setting, but with an Helix 7 gen 2.  The position of the transducer is really important. If it's mounted outside on an aluminium boat transom, it's best to have a metal mount on a composite plate that gives you the possibility of adjustment.  The plate also places the transducer  a half an inch from the transom and that helps with the reading.  For reading at speed, the sensitivity must be set low.  If it was working well before, maybe you hit the transducer and it's position has changed.  A slight angle at the back is best.  I can read the bottom with no problem at over  50 mph.

You might call Humminbird customer service and ask them.  They have a bunch of good techs.

Thanks for your replies. I've taken the boat out of the water and checked the transducers and their position. They look fine and in the proper position although when I mounted the Di, Si Transducer I mounted it level to the hull about 1/8" low. It was not set on a slight angle as you mentioned. I will try that. I think I'll give Humminbird a call and see if there is a different sonar transducer I should be using. I'm putting it back in the water tomorrow.  I'll update when I have more info.