Slow secondary replica redo performance

Hi sajidur07 --

Secondary replicas that are considerably smaller (you didn't include secondary replicas compute specs) in terms of compute power are most always going to have an issue with redo performance with that level of transactions.  You mentioned the secondary replicas as read-only replicas which implies that there is also a read/reporting workload consuming compute resources (which in turn adds to the redo queue issue).

Without right-sizing your secondary replicas, this will be difficult to fix.  My suggestions is to look at the wait statistics on the secondary replicas to understand which resources are most constrained (RAM, CPU, etc.) and start there with adding resources.  Take care.