Yesterday, I was in the hearthstone mobile app, and I went to mass disenchant my cards; I had over 17000 arcane dust according to the mass disenchant button. I clicked this button and game hanged/lagged. I closed mobile app and launched again. I went to my collection again to check results and saw that Mass disenchantment gave me only 13000 of arcane dust. 4000 of arcane dust disappeared.