Hi,
Are you using the latest firmware version? I was not able to reproduce it. The connection should be back when the WAN connection comes back.
I recommend updating to the latest firmware version. If the problem still exists, please give more information and provide the troubleshoot file. Before you generate the troubleshoot file, replicate the issue. Take a screenshot of successful pings via Wireguard, disconnect the WAN connection and wait for one or two minutes before reconnecting it to allow the router to reestablish connections. After the reconnection, take a screenshot of failed pings and generate the troubleshoot file.
Kind Regards,
Andzej