S9 Triple Board Failure Parameters

After working on a multitude of Asic miners it is still perplexing as to why a machine would drop 3 boards simultaneously. Ive compiled a basic list of reasoning and wondered if anyone eles has something to add to the list?

1: Bad Falsh
2: Faulty Control Board
3: Faulty Enet Port or Cable
4: Faulty PSU
5: Thermostatic Issue

Does anyone have any input on other reasons a miner might throw 3 boards simultaneously?