I thought this could be related to https://bugzilla.kernel.org/show_bug.cgi?id=199813. Indeed dmidecode -t 41 shows there are two interfaces for type interface 1 and two for 2.
** Bug watch added: Linux Kernel Bug Tracker #199813 https://bugzilla.kernel.org/show_bug.cgi?id=199813 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1908140 Title: Bond DHCP fails on Ubuntu Server 20.04 netplan To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1908140/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs