I fought with this for hours. In the end the only thing that worked for me was to comment out both ipv4 and v6 and just open the gate completely:
host all all all md5
I note there is a discrepancy in syntax between Postgres and Esri docs for ipv6 that may come in to play. Compare the suffixes, "%10/n" vs "/n":
[Esri] To allow any machines with an address beginning with fe60 to connect, you would add this line to the pg_hba.conf file:
host all all fe60::0000:0000:0000:0000%10/8 md5
[Postgres] An IPv6 address range might look like ::1/128 for a single host (in this case the IPv6 loopback address) or fe80::7a31:c1ff:0000:0000/96 for a small network.