I can only speak from my experience of working on these Mac Pro's. The majority of hardware faults I've seen have related to the video cards. Apple's propriety diagnostics will often pass, but colour grading with DaVinci Resolve Studio causes kernel panics, restarts, black screens or video artefacts. Most of these Mac Pro's I see are used for high end video production. We often have to substitute parts, then extensively test. One of the 2 video cards can be removed to aid diagnosis, but not the other with the SSD attached unless it's substituted. Other issues can be memory related, checked by substitution even if diagnostics pass the memory. These Mac Pro's can be very time consuming to work on.