Crossfire RX Vega 64 is very unstable while gaming. Several THREAD_STUCK_IN_DRIVER bsod errors while gaming or even while on the desktop.
BSOD issues have existed with Crossfire RX Vega 64 since 18.11.x drivers.
Workaround: Roll back to 18.10.2 with only one GPU installed. Then install the 2nd GPU.
Very unfortunate that the end of year drivers did not resolve the issues present since the November drivers.