Hello,
I'm not sure exactly what coul be hapenning, but I would suggest as a first troubleshooting step, try to capture this traffic on both interfaces of the ASA. Create an access list to match this traffic flow and then apply it to a capture line and then apply the captures to the ASA's interfaces.
access-list capture permit ip host host
access-list capture permit ip host
host
capture capin access-list capture interface inside packet-length 1520
This would be the capture to use in the inside interface, you would need to create another acl if there's NAT for the outside interface otherwise just create anothe capture line with the same acl and apply it to the outside interface.
Run a test and check you captures with the show capture command.
Start with this and try to determine if the traffic is being dropped in the ASA on the way back.
Hope this helps