Theres one big one that worries me about every cryptocurrency: a vulnerability that leads to the collapse of the blockchain.
This is something we havent seen yet and may never happen to Bitcoin, but Im convinced that at some point in the next few years, were going to see a blockchain vulnerability that compromises the system and brings the value to 0.
If a system like Ethereum or Bitcoin experienced an event like this, it would be absolute chaos for the ecosystem because most people dont believe its possible.