Try disconnecting the sensor from the hub when the unit is powered down. Then turn the unit on. If it says it can't find the sensor, then try to reboot without the sensor.

Then power down, and hook-up the sensor, see if it will fin the sensor then. IF it requires initialization identifying the sensor, go through that process and see if that solves the problem. I assume there are other sensors on NEMA 2000 system on its trunk?

Your wife's observation that main CPU "crash" and subsequent re-boot may be material.

OR: Could the terminal shunt (sometimes the sensor itself, like a masthead wind sensor has that built-in) have come to not be in-place for some reason?

OR: If it's not a NEMA 2000 connection, On the B&G new systems (maybe like Lowrance), the depth sensor is a "home run" to the CPU. If that's the case, check that input at the CPU.

(I realize that "nothing changed" expect the instrument stopped working. I'm just trying to help.)