Consider a dirmngr instance configured with "use-tor" in dirmngr.conf, on a
machine with an intermittently failing tor daemon.

when dirmngr fails to connect to tor's socket (localhost port 9050), it just
marks the host it was connecting to as dead.

At the very least, a failure to connect to 127.0.0.1:9050 should cause dirmngr
to emit some error messages specifically about tor to make it easier to debug
the problem. But i tend to think that if the tor daemon is not running, that is
more of a dirmngr-wide problem, and not something that should cause individual
hosts to be marked as dead.