TIME-WAIT
Networking
The state kept, for a minute or two, by the side that closed a TCP connection first. The four-tuple stays reserved so a straggling packet from the old conversation is not taken for part of a new one reusing the same values. It is correctness, not a leak: the state is time-bounded and goes away by itself. On a service that closes many connections ss -tan shows enough of them for the port to look occupied, hence the intermittent Address already in use on restart.
Also written: ss -tan, Address already in use