PID exists in netstat but does not exist in task manager
You don't need Task Manager for tracking this. Just run netstat -b which will display the exe associated with the PID..
Well, in my case killing all the conhost.exe instances owned by the same user as the initial process released the port.
(improved from @mfck's answer)
- kill all processes named
cmd.exe - kill all processes named
conhost.exe