Tested on 1.12.2 with Random Teleport v1.7.4 (build #20)
To easily reproduce, set the config to /rtp 4001 5000 -f -x 0 -z 0 on a world with a 4000 block world border.
Expected behavior: The plugin says it cannot find a safe location
Actual behavior: The player gets teleported outside the world border.