I ran into the same problem (Specific to W2K12R2 Server 2012 R2), I had the issue with both the 1.221 and the 1.229. On the same proxmox server I had installed a 2019 server with the 1.221 drivers. So I tried the 2019 driver on 2012 and it worked. (\virtio-win-0.1.221.iso\vioscsi\2k19\amd64\)
I am trusting that there is not a difference between versions.