Persistence none

This is normal behavior. By default, BigIP LTM balances TCP connections, not individual HTTP requests. Take note of 5 minute default TCP idle timeout. If you see that all connections go to same pool member even after 5 minutes since last request was made, then you have a problem that needs further investigation.

With OneConnect profile you can change this behavior so that BigIP will start to balance individual GET/POST/etc. requests within the same session but this is a double-edged sword - you will lose visibility of true client IP address in network stack and must rely on HTTP headers such as X-Forwarded-For to get client IP information in end-servers.

Using least-sessions or least-connections LB algorithm, you can achieve very good balancing results without OneConnect. You just need more concurrent clients to see those numbers even out nicely.