My practice attempt to decrypt a SHA-256 hash of an IP address

[royce]

no, it doesn't. there are no instances of .?1 or .?2

That's what I get for not escaping my '?' in my egrep. Then I have no idea why the OP got that as a hit.

and a "normal" IPv4 representation does not have leading zeros

I generated that hcmask file

"Normal" or not, they are accepted as perfectly valid in a variety of configurations and interfaces. Admittedly rare, but it's a thing.