I can't say much for Bukkit, but I found this in the Forge Docs: https://mcforge.readthedocs.io/en/latest/networking/simpleimpl/
Edit: Isn't Bukkit entirely serverside anyway? (Rhetorical question)
According to your latest.log you are using LiteLoader and Sponge, this forum is only for Forge/FML.
Using sites like Dropbox or mediafire is also discouraged.
Please read this thread:
If you have a world open, holding F3 and C for 10 seconds will crash the game as part of vanilla minecraft's debugging features. As for the launcher re-opening, while it's no longer automatic you can set it to remain open while the game runs by following the steps below.