The Lightning Network is a second-layer payment protocol that operates on top of the Bitcoin blockchain. It was designed to address some of the scalability issues facing Bitcoin by enabling faster and cheaper transactions off the main Bitcoin network. However, like any technology, it has its disadvantages.

One of the most sophisticated disadvantages of the Lightning Network is the routing problem. The Lightning Network depends on the existence of payment channels created between two parties. If I want to send Bitcoin to someone who is not directly connected to me, the payment must be routed through one or more intermediaries who have payment channels with both parties.

The routing problem arises when there are no available payment channels between the two parties, or the existing payment channels are not well-connected. In such cases, the payment cannot be routed, and the Lightning Network cannot be used. This can lead to increased complexity and cost for users, who may find it difficult to access some parts of the network

But then again this issue will be minor once mass adoption takes place :)