Why does my VPN Gateway say "Offline" with 100% packet loss

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I'm using a Wireguard config from ProtonVPN.

I started by setting up an interface and a peer in OPNSense WG, following this guide: https://docs.opnsense.org/manual/how-tos/wireguard-client-proton.html

Then, wanting to route all traffic on OPT1 through my external ProtonVPN service, I followed this guide: https://docs.opnsense.org/manual/how-tos/wireguard-selective-routing.html. Some steps here are redundant, but I read through it all to make sure I understand. I also performed the Optional Step 11 in this guide (Add a kill switch). I did not do the "Configuring IPV6" step. Nor did I do the "Dealing with DNS Leaks" step, as I am using ProtonVPN's DNS.

Everything seems to be working well. All my devices connected to OPT1 seem to be routing through ProtonVPN (`curl ifconfig.me` shows a different public IP), and all my devices connected to LAN are not routing through the VPN - which is as I intended. I achieved this by (per Step 8), adding a firewall rule to OPT1 to allow hosts to access to VPN tunnel, and putting this at the top of the firewall rules list. For completeness, I did not do this for LAN.

Although everything seems to be working as intended, my Gateways widget on the dashboard shows my ProtonVPN gateway that I created is "Offline", with 100% Loss. Why could this be? I'm worried that I might have configured something incorrectly.