Hello,
It would seem that the Conversation: The ashen scale with Ombre isn't available if you talked about The ashen scale with Tremor. The option simply dissapear.
I went back to a save file where i didn't talk to Tremor yet and i could see the conversation option with Ombre. But as soon as i have that talk with Tremor the option with Ombre just dissapear as well.
The required event 'Yellow like sand' is done on both cases.
Is it a bug ?