Login fails when using FQDN to access local Windows 10 shares

I have a Windows 10 Professional PC running 20H2 build 19042.685. I recently reformatted the PC and freshly installed this version. It was running the same or very similar version prior to the reformat. It is set up with local accounts (not Microsoft accounts), and uses workgroups. Prior to the reformat, I was able to access file shares using the FQDN (\\host.domain.name\share), as well as the IP and hostname. Now, I can access the IP and hostname, but the FQDN no longer works. If I sniff port 445 in Wireshark, I don't get any traffic when accessing the FQDN, but I do when I access the IP and hostname. If I connect to the FQDN, I get an Audit Failure Event ID 4625 in the Security log, with status 0xC000006D, sub-status 0x0. I am prompted for a username and password. No matter what username and password I give, it fails. I am not prompted when I open the IP or hostname. My router/firewall (Ubiquiti EdgeRouter Lite) is also doing DNS, and registers DHCP leases with DNS, giving the FQDN.

What am I missing? What can I do to troubleshoot this further?

I found a setting buried in System -> Rename this PC (advanced) -> Change... -> More...: Primary DNS suffix of this computer. Setting this to the appropriate DNS suffix made the login issue go away.