If a single locker will not open, or all of the lockers connected to a controller appear offline, then resetting the PoE injectors via power cycling may help restore the lockers connection to the Controller.
Locate the black power cables connected to the multibox in the locker kick. The black power cables are used for the PoE inejectors. Unplug each black power cable from the multibox, wait 10 seconds, and then plug each back in again. Any PoE injector visible has a small green LED on the top. The green LED should be on when the power is connected.
When the PoE injectors are reset, each locker will transition from Blue blinking to either Green or Red (depending on whether the locker is reserved or free). If the lockers continue to blink blue for longer than 2 minutes then a Controller reset is also required.
Swipe a card that is known to work or otherwise attempt to open a locker via the Smartalock App or kiosk PIN code. Watch for the door to open. If Locker still does not respond then try one of the alternative solutions below.
How to Restart the Kiosk iPad (Full Reset)
Troubleshooting frozen iPad kiosk panel (restarting kiosk fs app)