The market price for the whisky you are maturing may fall.
Your whisky may become difficult to sell if it has become too old, or too scarce, to be useful in a blend, while not being thought good enough to be bottled as a single malt.
Your whisky could be destroyed or stolen. In either case you would receive a payment from insurers, which would ordinarily represent the loss-adjusted true and fair value of your whisky, although this might not be as much as you thought it worth.
We cannot list all risks in the real world. The above are only some of the risks, and there may be others.