@Kevin BeccarisThank you for reaching out. I understand you are facing issues with you site-site Azure VPN Gateway where the even though the tunnel is up the traffic stops passing through.In order to pin-point the issue, I think it will help if you could follow the troubleshoot instructions below :
- Enable Diagnostic logging for the VPN Gateway and check if you can find any issue in TunnelDiagnosticLog for the VPN connection.
- Perform a packet capture on your VPN Gateway to get to know if the traffic is reaching the VPN Gateway or if the issue is related to the on-prem device.
- Check if the on-prem device is listed in the validated devices list here for Azure VPN.
- You can also try following the troubleshooting document here and see if that helps in resolving the issue.
Please let me know if you have any additional questions. Thank you!