Can be the silicon lottery.
That also happens if there is the slighest anomaly with cooler alignment or TIM application.
You could check it by taking the cooler apart but then warranty is void.

Initially, I saw reports of some VEGA cards having very bad TIM and users getting 6 - 10 C improvement by applying some good TIM. So I took one of my cards apart and installed a high end TIM. I didn't see anything wrong with the stock TIM and it looked exactly the same as the one I applied. Afterwards, I saw a slight increased temperature on HBM compare to before and compared to my other cards.

If you are serious about getting to the bottom of it, you could swap coolers between two cards and see what happens.