Electric elements do "rot out" and expose the nichrome wire to the water. The
grounding/bonding will cause the breaker to trip if you have a lot of minerals
in the water. I would suggest removing them and giving them a quick look. If
they show signs of cracks or corrosion, replace them. They are cheap.
This can be exacerbated by buildup of those minerals at the bottom of the tank.
If the bottom element can't "breathe" it will quickly burn out and there is
plenty there to short it to the tank.
I have a piece of 1/2" CPVC rigged up to fit on my wet/dry vac to suck this
stuff out.

OT ... has anyone used engine heat, via a double isolation heat exchanger to
heat water? That sounds like a "free" way to do it if you are running.