Survivable Sessions with multiple VPN Tunnels

We have 2 VPN dialup tunnels setup from a remote office to our data center.

Routing is dynamic via OSPF and working correctly.

We do have a number of very long lived connections (such as Remote Desktop sessions, SSH and other for example) that break whenever the firewall switches from the primary to the secondary VPN tunnel due to the WAN1 interface going down.

In the past we had Cisco DMVPN routers setup which are non-stateful and therefore the sessions would automatically resume across a different path. Now with the stateful Fortinets in place this is becoming more of an issue.

Yes, the primary circuit is somewhat unstable, but there isn't anything we can do about it at the moment.

I'm wondering if other people have come across the same situation and how it was resolved.