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.

Ok, thanks. I'll give it a try when I get the chance.

v1.7.4 is outdated and not supported anymore. If you want to use this on such an old server version then try with build 61 which is the latest v2 version which still supports 1.12.2.