Learn English – Using *not* in a sentence

You can say "The tragedy continues to take lives," which means the exact tragedy has happened, but some people involved in it die later in a hospital, for example. Or the tragedy, as such, continues, so it can continue to take lives.

When you say "Crowd tragedies continue to take lives all over the world." you mean tragedies in general and not specific tragedies, so they cannot continue to take lives. Only specific tragedies that actually occurred can continue to take lives.

In your case, "continue" is hanging, because it is not clear to which exact tragedy it refers.

So, you can simply say:

Crowd tragedies take lives all over the world.

or, if you want:

Crowd tragedies often take lives all over the world.

And yes, by saying that your sentence is hanging, your teacher very likely refers to a dangling modifier. This is a broad term, which refers to all cases in which it is not clear what a certain word in the sentence describes or modifies.