Guild Wars 2

In the first mission of Tangled Path LS where you, Rox and Caithe go find the zephyrites to know the location of the Master of Peace, I’ve been unable to trigger the challenge mode in order to get Dancer in the Dark achievement… I’ve looked at different video/guide to find the location in case I’ve skipped it but it just look like it doesn’t show up in my instance. Is it a general bug for everyone or just for some players?

This is happening to me too.
I tried this achiev two times, but now the Mode no longer appears.

EDIT:
Well… I got frustated and started to do other achievs. Later, I tried the Dancer again and the Challenge Mode was there . I guess starting a new story mission worked out.