Authorities mark every relay as down-for-an-hour at every restart
In https://trac.torproject.org/projects/tor/ticket/1035#comment:40 I reported
Jul 07 14:08:27.000 [info] rep_hist_note_router_reachable(): Router BFA1BA13CAC96F8C13689FE1FDC65359ED6AC6D7 still seems Running, but its address appears to have changed since the last time it was reachable. I'm going to treat it as having been down for 7200 seconds
I see those in practice on moria1 still:
$ grep -i "still seems" moria1-info|grep "Feb 12"|wc -l
501
The issue is this code:
addr_changed = at_addr &&
tor_addr_compare(at_addr, &hist->last_reached_addr, CMP_EXACT) != 0;
port_changed = at_port && at_port != hist->last_reached_port;
where last_reached_foo always starts out empty, so the first comparison always shows a change.