Most likely the ear for screw to go through from the reflector snapped off. There are total three (two on one side and where you pointing with finger one more). This is a great opportunity to replace those reflector with LEDs (so they shine when you break or have light on or both). There many sold on eBay. Here it is a set I have for sell on eBay as I bought two different one to decide which one I want to install.
LED Rear Tail Bumper Fog & Break Lamp Toyota Land Cruiser 200 LC200 2016-2017 | eBay
To install you need to remove the bumper. The process takes roughly 10 minutes (20 min if you have not done it before). I hope this helps