MI50 16GB — colorful noise/rainbow artifacts only after installing AMD driver

I have a Radeon Instinct MI50 16GB HBM2 (Vega 20) flashed with Radeon VII Pro VBIOS.
The problem only appears after installing/loading the AMD driver.
Before the driver:
BIOS image is completely clean;
Windows works normally using Microsoft Basic Display Adapter.
After the AMD driver loads and Windows reaches the desktop, the screen becomes full of colorful noise/rainbow artifacts (hundreds of colored pixels). The PC itself keeps running and Windows does not freeze.
GPU-Z detects the card correctly:
Vega 20;
16GB HBM2 Hynix memory;
PCIe x16.
Monitor connection:
mini DisplayPort on the MI50;
mini DisplayPort to HDMI adapter.
I tried reinstalling drivers. The artifacts appear exactly when the AMD driver activates the card.
Possible causes I am considering:
driver incompatibility with Radeon VII Pro VBIOS;
miniDP-to-HDMI adapter issue;
wrong refresh rate/display mode;
HBM2 memory instability when full clocks are enabled.
Has anyone experienced something similar with MI50/Vega 20? Any advice on what to check would be appreciated.