It happened to me, but here is what I did:
Copy "Lonely Cave" From the regular FH folder
Paste it in FH+ "fhmaps" and restart the game
Actually, if you're allredy playing FH+, click "Reset Home" or something like that, then "Lonely Cave" should appear. Maybe that could help
![Tongue :P](https://feral-heart.com/smf/Smileys/default/tongue.gif)