The sending address could not be used important
The engine could not bind to the local address it was told to send from.
In detail
Entirely our side: the address has gone, or something else holds it. Whether it is retried or fatal is one of the switches packed into capacity.flags. For a fleet this is a state worth alerting on rather than counting: it means a node's address list and reality have diverged, which also makes every warm-up plan on that node wrong.