I have not seen anyone post about this, excuse me if I missed it somehow.
I cannot do the ‘Hidden Arcana’ achievements from ‘Echoes of the Past’ because the dialogue that leads to the hourglass does not appear. Ogden only discusses the Elder Dragons with me.
Is this a common occurrence?
Someone helped me do this instance, we failed to get me one of the achievements. So, I decided to go in again. Lo and behold, going in with another person fixed the instance for me. If you have the same problem, try that!
There is a thread about it on the bugs-forum :
https://forum-en.gw2archive.eu/forum/support/bugs/Hidden-Arcana-Issues-merged/
Maybe you could add your experiences, too? So that they might have enough data some day and fix this