All I can say is be ready to RMA or have a look at the Overclock.net article
HERE for troubleshooting.
In my experience, this is a lost cause. I phoned Asus today and reached 'Tech 3 Priority' Support (whatever that means) to RMA my
second ThunderBoltEX 3 card and the rep specifically said:
There are no problems with the Asus ThunderBoltEX 3 Card. We have not heard of, or know of any issues with the card.I asked, "Have you looked online in any forums? There are issues being reported everywhere. I'm having to send my 2nd card in for RMA in the span of 2 months."
Asus rep response:
There aren't any problems being reported with the Asus ThunderBoltEX 3 Card, but thank you for bringing this issue to our attention.Worst part of the RMA, because the card was included with my X99 Deluxe II purchase, they require I send the motherboard in as well for testing. I just got my motherboard and thunderbolt 3 card back from repair from the previous RMA 3 weeks ago, and now I have to send it in again.
Thanks Asus.