Loss of internet connection in Linux VMs after reboot

[tobi]

I have a strange issue with my OPNsense (v22.1.10) installation hosted on a Proxmox 7 server:
My LAN consists of multiple VMs (Windows and Linux). The Windows VMs work fine and are able to access the internet (even when rebooted). But if I reboot the Linux VMs after the reboot no more internet connection is possible.
This situation lasts until I reboot the OPNsense VM. After that the Linux VMs are able to connect to the internet again. But once the Linux VMs are rebooted once more then the connection is broken again !?

Does anyone know which could cause these problems ? I would be thankful for any idea how to analyse the problem. I don't know what to check to solve this ?

[Patrick M. Hausen]

IPv4 or IPv6? A freshly booted system configuring IPv6 via SLAAC might take a while until the next router advertisement comes around ...

[tobi]

It's IPv4