I was puzzled that nut-server.service was not starting on my
workstation. I had
installed it to use with HomeAssistant.

I tracked it down to the service file not requiring
network-online.target, but
only network.target.

I replaced all the instances of network.target with
network-online.target and
now the nut server starts correctly every time.

I checked nut-server_2.8.1-3.1+b1_amd64.deb and nut-server.service still
only
uses network-online.target

This may slow some installations that have static IP assignments.

Dear Maintainer,

It does not fail to start, but simply doesn't listen on the IP address (since it's not there yet). It seems to be a deliberate choice from upstream since the service file has a comment saying:

# The `upsd` is a networked service (even if bound to a `localhost`)
# so it requires that the OS has some notion of networking already.
# Extending the unit does not require *this* file to be edited, you
# can instead drop in an additional piece of configuration, e.g. to
# require that NUT data server only starts after external networking
# is configured (usable IP addresses appear in the system) you can
# add a `/etc/systemd/system/nut-server.service.d/network.conf` with:
#   [Unit]
#   Requires=network-online.target
#   After=network-online.target

But this still feels like a bug here since that suggested configuration is required for the LISTEN configuration to be respected.