The issue is that the module "minecraft-packets" was updated from 1.5.0 to 1.5.7 with a breaking change. For a temporary fix you can either rename the versions "1.8" to "1.8.8" inside /node_modules/prismarine-proxy/src/instant_connect_proxy.js or alternatively downgrade minecraft-packets to 1.5.0.

Another issue will occur because the encryption fails, the only workaround I have found so far is disabling "online-mode" in /node_modules/prismarine-proxy/src/instant_connect_proxy.js (this is the authentication between your game and the proxy). Beware, this is a security risk if ran on an exposed network/server since anyone can now connect to your proxy.

source and more info: https://github.com/PrismarineJS/prismarine-proxy/issues/42 https://github.com/PrismarineJS/prismarine-proxy/issues/40