In Cluster, secondary node will not process transit packets. You may have to change the WAN connectivity such that both upstream gateway should reachable via primary node and secondary node so that cluster failover will not cause any issue. Terminate WAN connectivity to a switch and connect both nodes to that switch. Use seperate VLANs for each WAN connectivity and use reth interface on SRX
Example:-
ge-0/0/3 & ge-1/0/3 --> reth0 -->[valn10] Switch [vlan10] --> WAN1
ge-0/0/4 & ge-1/0/4 --> reth1 --> [vlan20] Switch [vlan20] --> WAN2