I just build an old Gigabyte Vega 56 Gaming OC. Almost the time it works great. But sometime its fan runs at full speed, the monitor turns black but the music still plays! Look at GPU-Z's log file and I see its hotspot temp is 511*C !!! And the VDDC is < 0!!! Everything else works normal
My PC: I5 8600K, 16GB, Asrock z370m-pro4, Windows 10 pro 1903, Radeon driver v19.9.1. I use WC for this card and its temps are rarely go > 80*C