Dialup VPN Interruption

Hi folks I ve got a problem with Dialup-Connections. My Dialup-Clients (Forti 30E) connecting over LTE to the hub which works fine. I configured the VPN Tunnel to stay up permanently. However the LTE connection gets interrupted from time to time e.g through provider. The problem now is that after the interruption the tunnel comes not up properly with the error reason: "peer SA proposal not match local policy" 

Any suggesion?

Is there a way to delay the new VPN-connection?

Thanks