Do you have a link-local v6 address on that device? My first attempt `ping ff02::1%enp9s0` didn't work because I use VLANs and don't actually get addresses on the base device, using the VLAN virtual device (in my case `ping ff02::1%lan`) worked for me.
Yea I figured -6 was superfluous but I put it in because another commenter made a big deal out of ping vs ping6 (a distinction that's been gone in Arch for a while).
I do have a link local address directly on that NIC. I also use VLANs sometimes, but none are configured right now on this link. Slightly edited below to hide my MAC but:
$ ip -6 address show dev eth2 | grep link
inet6 fe80::aef0:b837:fafa:fefe/64 scope link noprefixroute
The same command works fine on my Debian and OpenWRT boxes, but not on my Arch desktop.
You shouldn't need `-6`, given it's a v6 address.