Just about anything can cause a sub to die. I can speculate.
Bad design leading to poorly specified parts like power supply capacitors or even $0.02 parts like resistors.
Poorly manufactured boards or assemblies like drivers.
Poorly documented instructions from engineering to the shop floor.
Vendor parts that don't meet spec but pass functional tests during production. This is a tough one. It's expensive and time-consuming to screen parts.
Incomplete production testing. "Just build it and ship it".
I worked in hardware factories for 20 years. Another 10 years in a software factory.
