A secure site login is failing with dual-WAN

[Benconnected]

We just set up a Dual-WAN configuration on PFSense 2.3.1. It broke a specific HTTPS website by randomly kicking users out of their sessions, or not letting them log in at all. When I disable one WAN, it starts working again.

I assume it's because the site is tracking the session IP which changes because of the dual-WAN and kicks them off. Is there a way to route all traffic for the specific domain or IP through only one WAN?

I want to maintain load balancing and failover for everything else.

[dotdash]

Create a failover group and a load balancer group. Have a rule matching https with a failover gateway before the rule with a balancer gateway.
You could also try the sticky option, but I haven't played with that in a long time.