Can’t mount shares after windows update

On a 192.168 subnet, my Ubuntu 22 fileserver serves folders to a mac and to a Windows 10 host. After a windows update and subsequent reboot on 2025-03-09, suddenly Windows can no longer mount those folders. (Nothing changed on Ubuntu or the mac: the mac still mounts folders ok.)

• In File Explorer, doubleclicking on the icon of one of these
  unmounted shares yields a popup “Restoring network connections …
  The local device name is already in use. This connection has not
  been restored.”

• From Windows I can ping and even (via WSL2) ssh to Ubuntu, by hostname or by
  dotted quad.

• The /etc/hosts and driversetchosts files are compatible and
  unchanged from before.

• net view \ubuntuhostname fails with System error 53 has occurred.

• net use \ubuntuhostname fails with System error 1231 … The network location cannot be reached,
  which is silly, because an ssh session is running from Windows to Ubuntu.

• Turning off the firewalls for the public and private network doesn’t change the failure of net view and net use.

What might have changed on the Windows host? How can it once again mount what it used to?