Some advice, please, on this network problem:

There are 3 Win 10 hosts on my home network: BOUDICCA, GILGAMESH and HIPPOLYTA.
File Explorer/Network shows all three hosts from any other.
All three hosts can ping one another, by name and by IP address.
On HIPPOLYTA, clicking either of the other two in File Explorer accesses their top-level directories.
On BOUDICCA, clicking either of the other two in File Explorer accesses their top-level directories.
On GILGAMESH, clicking BOUDICCA accesses its top-level directories; clicking HIPPOLYTA gives "Windows cannot access/network path not found".
All three hosts have Network Discovery turned on, and "Use user accounts and passwords" selected.
Router is a Netgear R7000, and its Attached Devices page shows all three hosts as connected, with IP addresses in agreement with what they show in ipconfig.

TIA...