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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You're only looking at one temp sensor. I know because I have the same issue with mine, where gpu temp looks low but there's more under the surface. If you have software like hwinfo64/gpu-z, you may notice some entries for performance limit. This will tell you whether it's thermal or power limit hindering your performance. The general consensus seems to be memory overheating with OC, and I've noticed thermal throttle being the performance limit even with low GPU temp reported in afterburner.