In order to create an IPsec VPN between two sites, I proceeded as follows :

Site A: Pfsense with two WAN1 and WAN2 interfaces (Failover - Gateway Group)
Site B: Pfsense with a single WAN interface

I configured IPsec on Site A to choose the gateway group (WAN1 as primary link - WAN2 as second link).

I configured two site-to-site VPN separatly on site B in responder only mode to etablish connection with both WAN1 and WAN2 addresses on Site A

1st case: The two WAN links of site A are UP, IPsec establishes the connection and everything works normally (OK)

2nd case: I disconnect my primary link WAN1, the IPsec switch well on WAN2 to establish the connection again (OK)

3rd case: when I reconnect my primary link WAN1 IPsec always keeps its tunnels establish with WAN2.

Thanks for your help,