I went for a Elite clan quest. I had to get 5 legendary artefacts with speed sub stats. I had over 400 material in the forge. I created around 10 artefacts and then suddenly the 400 material were gone !

Furthermore, if I try to get new ones, they don't appear in the Forge. 

So, I can't finish my quest. Besides, I lost all the material I had won battle after battle. That's a hard blow ! What should I do ? Thank you.