Going from memory.

If you have a specific bottom depth selected, say 40', then uncheck the setting "manual". Can't remember which menu that is in. On these units according to the manual, when manual is selected it just sends the signal to that depth. Could be why you are loosing the bottom reading.

Unselecting manual on these units does not put your unit in full automatic mode. I think maybe that is a setting called advanced mode.

Might see if the problem occurs on auto depth.

If lowrance offers to send you a new transducer (free), I have haver had that fix the problem, however it is nice to have spare transducers.

Sometimes the depth will blink on these units. If it blinks for more than thirty seconds a lot during the day I think it makes the unit unusable. I don't know how often and how long yours is blinking.