I was using Beta+ as the generation type and noticed it wasn't compatible with the cave generation. Is there any way of fixing this by myself, or is this a feature either you or the author of that mod has to implement?

I love this mod. Would be awesome to use this alongside Beta+

That would be up to the Beta+ dev. Taking a quick look at his 1.12.2 code, it seems like it should be a fairly easy change to allow for other cave mods to work with it. I would throw this up on their issue tracker.

Edit: Seems they are done adding features to 1.12.2, though this is just copying one line of code to add the forge cave event back in so might be worth a shot.