From https://my.f5.com/manage/s/article/K000152647 : LB first choose origin pool, then checks cookie and it's hash inside chosen origin pool. Because of that, you can observe that requests from one client with stickiness cookie enabled can be load balanced to multiple origin pools.
To avoid that, you can use one origin pool with multiple IPs instead of multiple origin pools.

This seems counterintuitive. The option to select cookie based stickiness is within the load balancer settings, but cookie based stickiness is not possible via the RE -- It happens in the origin pool. The origin pool does not have a cookie based stickiness option within the load balancing algorithm section. This limitation means that we have to put to put origin servers which are in different regions into the same origin pool and use the CE to load balance them, instead of using the RE to do this.