I can replicate this issue at will.
If i remove the linux bridge vmbr0 -> bond0 and reboot the default gateway on bond0.200 lives
if i added back the vmbr0 and rebooted the unit the default gateway disappear.
root@compute-200-23:~# pveversion -v
proxmox-ve: 8.2.0 (running kernel: 6.8.4-2-pve)
pve-manager: 8.2.2 (running version: 8.2.2/9355359cd7afbae4)
proxmox-kernel-helper: 8.1.0
proxmox-kernel-6.8: 6.8.4-2
proxmox-kernel-6.8.4-2-pve-signed: 6.8.4-2
ceph-fuse: 17.2.7-pve3
corosync...
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If i remove the linux bridge vmbr0 -> bond0 and reboot the default gateway on bond0.200 lives
if i added back the vmbr0 and rebooted the unit the default gateway disappear.
root@compute-200-23:~# pveversion -v
proxmox-ve: 8.2.0 (running kernel: 6.8.4-2-pve)
pve-manager: 8.2.2 (running version: 8.2.2/9355359cd7afbae4)
proxmox-kernel-helper: 8.1.0
proxmox-kernel-6.8: 6.8.4-2
proxmox-kernel-6.8.4-2-pve-signed: 6.8.4-2
ceph-fuse: 17.2.7-pve3
corosync...
Read more