@fabian
I just ran into this problem myself
Installing pve-kernel-4.13.8-3-pve_4.13.8-30_amd64.deb from pve-test seems to have resolved the issue.
I would be happy to give Proxmox one of these cards to put into the test servers.
Would you like me to ship it to you?
please contact office@proxmox.com for test hardware inquiries