Load Balancing issue - Source Address Persisantence

with source Ip address peristence, you must take care of the netmask, as the persistence record is created based on that. If 2 IPs (let's say 10.1.1.10 and 10.1.2.20) are in the same defined netmask (for ex. 255.255.0.0), they will both use the same persistent record and hence, be using the same backend server. You can check the created persistent record with command

tmsh show ltm persistence persistence-records