errdead?

[Karl Kleinpaste]

That's errdead(1M-att) babbling at you, trying to find buffered error
messages that presumably would not have been flushed by the system
immediately preceding a crash.  It's invoked without args in /etc/rc,
and stares at the last dump in its search.  The "unreasonable"
diagnostic is errdead telling you that whatever it found in the dump
area is not considered a real dump; it found a dump time there which
was not within 3 days of "now," so it abandoned the effort.

It would appear that your system did indeed fall as hard as possible,
without time to execute a dump.  No clues...

--Karl