Solution: arpresolve: can't allocate llinfo for <ip> on <interface> after 23.01 upgrade

[MichelZ]

So, after upgrading pfSense to 23.01, we had an issue that IPSec VPN Tunnels to Azure did connect, but no traffic was flowing.
P1 and P2 did show healthy.
They are setup as IKEv2, VTI/Routed Tunnels

After some investigation we found these error messages in the System Logs:
arpresolve: can't allocate llinfo for <ip> on <interface>
Where <ip> is the IP of the Remote Gateway.

Under System -> Routing -> <VPN Gateway> we had to enable Use non-local gateway through interface specific route. (under Advanced Settings at the very bottom).

This allowed traffic to flow again.

Just in case someone else encounters an issue like this.