Multiple unwanted default routes being added automatically

[ianthrive]

How do I prevent default routes from being added automatically?

The default route that actually ends up being used breaks internet connectivity.

I would expect to only have:

default via 10.55.47.1 dev vmbr0 proto kernel onlink
10.55.47.0/24 dev vmbr0 proto kernel scope link src 10.55.47.5

But I am getting this:

root@spock:~# ip route
0.0.0.0 dev enp129s0f0 scope link
default dev enp129s0f0 scope link
default via 10.55.47.1 dev vmbr0 proto kernel onlink
10.55.47.0/24 dev vmbr0 proto kernel scope link src 10.55.47.5
169.254.0.0/16 dev enx9af1a47b7437 proto kernel scope link src 169.254.29.60
169.254.0.0/16 dev enp129s0f0 proto kernel scope link src 169.254.147.7

root@spock:~# systemctl restart networking

root@spock:~# ip r
default via 10.55.47.1 dev vmbr0 proto kernel onlink
10.55.47.0/24 dev vmbr0 proto kernel scope link src 10.55.47.5
169.254.0.0/16 dev enx9af1a47b7437 proto kernel scope link src 169.254.29.60

root@spock:~# sleep 20

root@spock:~# ip r
0.0.0.0 dev enp129s0f0 scope link
default dev enp129s0f0 scope link
default via 10.55.47.1 dev vmbr0 proto kernel onlink
10.55.47.0/24 dev vmbr0 proto kernel scope link src 10.55.47.5
169.254.0.0/16 dev enx9af1a47b7437 proto kernel scope link src 169.254.29.60
169.254.0.0/16 dev enp129s0f0 proto kernel scope link src 169.254.21.87

root@spock:~# pveversion 
pve-manager/8.2.4/faa83925c9641325 (running kernel: 6.8.12-1-pve)

root@spock:~# cat /etc/network/interfaces

[... snip ...]

auto lo
iface lo inet loopback

iface eno1 inet manual

iface enx9af1a47b7437 inet manual

iface eno2 inet manual

iface enp129s0f0 inet manual

iface enp129s0f1 inet manual

auto vmbr0
iface vmbr0 inet static
        address 10.55.47.5/24
        gateway 10.55.47.1
        bridge-ports enp129s0f0
        bridge-stp off
        bridge-fd 0

source /etc/network/interfaces.d/*