How did you arrive at the conclusion it's not thermal throttling?
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Cause the core clock drops to 930 mhz as soon as the memory is above +400 . Card temp hovers around 45-50c.

When a card thermal throttles it at least gets high enough to produce heat , my trio x does not even achieve that.

I experienced today my friend xc3 ultra thermal throttling and its not at all how my card behaves . His card hit 99mhs and stayed there for 5 min before throttling and crumbling down to 85 mh while temps were reaching 70C.

Pretty sure its a power limit issue . Some have fixed that by flashing the bios with a different brand bios with higher power limit .
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No it's not. You can confirm if it's throttling or not in gpu-z perfcap reason.
The temps that you see are core temperature and ethash doesn't pound much on the core but is hard on memory and GDDR6X runs really hot. Nvidia has the memory temperature monitoring enabled but haven't exposed it to users.  Most likely your card is throttling itself.