ASA won't respond to pings from different subnet

The ASA does not respond to pings to its interfaces that come from a different subnet to that configured on the interface. For example, a ping to the OUTSIDE interface IP from a host on the INSIDE interface will fail. Similarly, a ping from a host on the INSIDE interface to the DMZ interface will also fail.

https://community.cisco.com/t5/network-security/asa-9-1-2-drops-ping-icmp-codes-0-8/m-p/2672003