Xdebug tcp port opens only once

Open a php project

• click debug, but does not launch your https server.
• run nc -vz localhost 9003, where 9003 is the port configured in Preferences.

  % nc -vz localhost 9003
  Connection to localhost port 9003 [tcp/*] succeeded!
  

  So far so good.

• Click the Finish debugging session button. The new help with Xdebug version 3 shows up (great! the netbeans icon is not on top left hand corner of the modal box on macOS, see screenshot)

• Click debug again:

  % nc -vz localhost 9003
  nc: connectx to localhost port 9003 (tcp) failed: Connection refused
  

It seems NetBeans does not re-open the socket.