Many of the 2012s with bad SATA cables we have checked in have had sporadic behavior where the system will slow down dramatically, then temporarily run normally, then repeat the process over again, and eventually the cable just gives out. Quite a few customers have mistaken this for App or OS corruption and have tried reinstalling Apps or the entire OS, which obviously does not fix the issue if it is a cable (or physical disk) failure.
I agree 100% SMART verification is the way to go - it's not perfect, but in many cases it not only predicts HDD/SSD failure, but can predict the SATA cable failure as well.
Werd.