ipsec net to net over different ISP not working

i have a very simple problem:

my network has UTM A, UTM B and XG C

UTM A has several ISPs (ISP1, ISP2, ISP3), ISP1 is the topmost active connection in uplink balancing

there's a ipsec tunnel between A and B and works ok.

there's also a tunnel between A and C and also works OK.

now ISP1 has been having issues and it's losing packets etc etc, so i want to move the tunnels to the other ISPs to solve this.

i create and define the tunnel using "local interface ISP2"(i'm not even using additional IPs, just the base one defined in interfaces), edit the remote gateways on the remote endpoint, all ok.

The IPsec Tunnel connects ok but NO TRAFFIC PASES, either from B to A or from C to A.

i then redefine the tunnel using ISP1 and works perfectly(i only change the remote gateway in B and C to match the old ISP and the local interface in A to match old isp again) and starts working instantly.

¿what do i need to do to build ipsec net to net tunnels on different interfaces?.

i'm running 9.411 and XG 16.5 MR2