I'm not sure if I'm being helpful or not, but please accept my thinking below, possibly leading to some help.
I happen to have this same card, a least I think I do. It's a
Gigabyte Radeon R9 280X, either rev2 or rev3, I can't tell it only from the picture attached. I've got a rev 2. It's printed on the PCIe connector plate on the card.
It's a
250W TDP card, and in ypur config it seems to be powered only by 2x mini 6-pin connectors from the cMP motherboard according to attached picture. That would not be enough to operate the card at some high performance and power demanding situations. cMP mini 6-pin can give 100-110 without shutdown I have read. 2x is 200W-220W before cMP self-shutdown, plus the approx 30W from the PCIe slot. We are in the ballparks of a cMP self-shutdown already.
I really don't know if that too low of a power feed to the card would have caused this mentioned and unexpected behavior of the fans not operating normally or not, but it might have.
GPU card TDP is 250W and the card is measured to consume a lot more than that in some
tests, so it would need to be fed with more power than just 2x mini 6-pins from the backplane.
My card seems like yours, doesn't it?
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