Hello Saurabh,
Before the NAT rule was checked after the ACL verification.
Now it backwards. The asa receive the traffic on the outside, performs the Un-Nat and then checks the ACL.
That is why you need to use the private range on the outside ACL.
Do you understand?
Regards
Julio Carvajal
Senior Network Security and Core Specialist
CCIE #42930, 2xCCNP, JNCIP-SEC