|Once a given device, be it wifi or ethernet connection, has been given a reserved address, it will use "that" address each time. The router will assign that address for that device.|
If you reset the router, by pressing the reset button which takes the router back to factory settings, you will need to re-enter any changes you made to the router's settings prior to the (factory) reset. This includes reserved ip addresses, changes to the router's SSID, passwords.
Simply rebooting a router does not delete changes made. Likely the router may reboot following the creation of ip rserved addresses, or some other changes/additions. Usually it will advise you of this.