The issue is that LN trying to be a mesh network means it cannot scale. The creators admit the whole thing could become disfunctional somewhere between 10,000 to 1 million users of LN.

It is because the path changes from each hop have to be relayed to everyone kn the network. Eventually there is so much useless information being relayed that nodes cant process it.

This is the crux of the unsolved problem that is Mesh Network Topology, likely cant be solved in any sense for LN until tech is more advanced and better internet/cheaper server costs, and even then probably something less than 1 million could use it at once without bogging down system.