@hepa_s

I have the boot issue you're having, but on a "main" Vega which is plugged to the monitor itself.

By putting it behind an intel GPU like you did, the Oldcomer softpowerplaytable boots fine.

Instead of putting it stock did you tried to overvolt a bit in a custom powerplaytable ?
I think if you put 920-930mv in each states it should help the card booting, or just adding like +10% power target.

Do you use xmr-stack-amd, 2 threads/cards like it's explained page26 (2016-1600) for the 1850h/s ?

Haven't tried to monero yet, was already happy to have 4 R56 (flashed at 64) softpowermodded on main ETH at 173MH @750w at the wall.