Default Gateway disappearing for DHCPv6

[Sempiterna]

I'm experiencing a strange problem with my DHCPv6 setup. All my servers (Windows and Linux) properly receive a few IPv6 addresses from the DHCP servcer running on Opnsense, and are able to access the outside world (e.g. ping google). But after a while (30 minutes or an hour) the connection is severed and ping is no longer possible (Network is unreachable).

During my trial and error investigation process i found out that when this happens, the default gateway has disappeared from the route (both in windows and linux). Trying to renew the lease does not result in the default gateway being re-added. It does work when i force the network interface (networking) on the clients to restart or restart the client server.

The strange thing here, however, is that VMs which run on the same node/host as the Opnsense VM do not seem to experience this behaviour. 

Does anyone here have an idea what might be causing this? This IPv6 network is running on a Hetzner vSwitch. Maybe that vSwitch blocks 'something'?.

[Maurice]

DHCPv6 does not provide default gateway information, that's what Router Advertisements are for. And these might get blocked by your vSwitch.

Cheers
Maurice

[Sempiterna]

DHCPv6 does not provide default gateway information, that's what Router Advertisements are for. And these might get blocked by your vSwitch.

I thought about that as well, but the clients do receive the default gateway when they get their initial DHCPv6 lease. It's also enabled in the Router Advertisements within Opnsense.