Comment 4 for bug 1933402

Hmm,
to further corner the failing code.
1. is this failing in e.g. json output as well?
 $ ip -j -p a | grep altname
2. if you set an additional altname is it ok?
 $ sudo ip link property add dev enp2s0f0 altname mytest
 $ ip a | grep altname
3. try more names
  $ sudo apt install netsniff-ng
  # Depends on your kernel headers
  $ sudo /usr/bin/bash -x /usr/src/linux-headers-5.11.0-22/tools/testing/selftests/net/altnames.sh

If #2 & #3 didn't fail we need to find who adds these bad altnames and how it does so.
I haven't found a good interface to cross check, systemd/udev seems to do that.
So it might come down to debugging systemd/udev while hot-plugging one of those devices?