I've had my ASUS ROG Strix Vega 64 since January 2018 and just recently (August/September 2019 maybe?) begun having issues with both of my monitors blacking out, audio seems to still be playing, but hitting caps/num locks on the keyboard eventually stop toggling the identifier light and I hard reboot the system. The fans on the GPU will also spin a few hundred RPM faster than normal occasionally which seems to coincide with a crash unless I underclock the GPU.
This used to happen on my ASUS Crosshair VI Hero & Ryzen 7 1800X system and still occurs on my new ASUS Crosshair VIII Hero & Ryzen 9 3950X system. Below are any BIOS version info I could find for both motherboards. If there's any other information that might be helpful I'd gladly help out.
I've also attached a screenshot of the performance tab in the driver when the GPU fan spins up.
ASUS Crosshair VI Hero
BIOS Version: 6201 x64
BIOS Date: 2018-05-29
EC1 Version: MBEC-AM4-0310
EC2 Version: RGE2-AM4-0106
LED EC Version: LED-0116
KeyBot Version: KBOT2-ROG-0122
ASUS Crosshair VIII Hero
BIOS Version: 1201 x64
BIOS Date: 2019-11-18
EC Version: MBEC-X570-0218
LED EC1 Version: AULA3-6K75-0202
ASUS ROG Strix Vega 64 (From HWiNFO64)
Video BIO Version: 016.001.001.000
SMU Firmware Version: 5.28.20