I had a similar issue, at first I thought it was because Im running 12 gpu per rig and its just drivers arent stable.
But eventually found out that I needed a dummy plug or a monitor to be attached to the miner.
It didnt make sense, because I had other rigs running fine.
Im using something like these now:
https://www.aliexpress.com/item/Built-in-1080p-Chipset-Converter-HDMI-to-VGA-with-Audio-Cable-Micro-Mini-HDMI-Male-Adapter/1785843152.htmlThey are cheaper than the dummy plugs and works just as good.
Other issue I had, was undervolting, one of my cards was acting funny, all my other identical cards were running with the same undervolting (100+ cards), but this one needed an extra 50mv to be stable even at lower clocks.