Hmmm. Does it work for you with clips? The hotkey triggers a script that literally finds the currently selected clip tile in the list on the left and then emulates a click event on the next or previous clip tile. So it should not matter if it is clips or alerts in the list. If this script is failing somehow, there may be an error in the console. Press CTRL + SHIFT + I to open the browser's developer
tools (F12 instead, if on a Microsoft browser). In there you should find a console window. Once you have this open, refresh the page and take note of any errors. Proceed to play a clip and press the next/previous hotkeys and see if any errors appear at that point.
Also, which browser are you using? I only tested with Chrome so far.