Two possible causes:

Temperature change: A sudden temperature shift can cause brief condensation between the crystals. This disappears on its own within a short time.

Water exposure: If water has entered the piece, the sand will dampen and a mist may form. Leave the piece in a dry place — it will dry with time, but this can take weeks to months, particularly with salt water. This applies especially to AKIN First Series pieces which are not water-resistant.