Sapphire RX480 OC+ thermal throttling

Hello guys!

I have a rig of 6xSapphire RX480 8GB OC+ and one of my cards is throttling at 60 degrees.
I have set Claymore to keep it at 56 degrees, which seems to solved the issue. It is still slower by 0.1 than the others, but that's fine.

They use exactly the same BIOS and settings.

Could you guys help me with that? I didn't seem to be able to find the cause of the problem by myself.

Thanks!