They are not errors, they are debugging messages.
The first message means that an arp reply with new information
arrived, but cannot be immediately recorded into ARP table,
because someone already updates it,
so that this arp reply is recorded into backlog.
It is normal, but pretty rare event.
Really we might drop this reply, that is even more correct.
When the previuous update has been finished, we process backlog.
The second message means that someone has already created the entry
with the same ip address & device to this time and backlogging
were vain efforts!
(Note that the sence of "was born dead" message would be slightly
different, provided it followed "arp_find: ... backlogged"
or "arp_cache_bind: ... backlogged")
Alexey Kuznetsov.