Likely the thread that joins the client player to the client server. The problem is, the more Lag your Modpack does while launching a World, the more this Issue happens, which is why CoFH Core causes it A LOT.
Likely the thread that joins the client player to the client server. The problem is, the more Lag your Modpack does while launching a World, the more this Issue happens, which is why CoFH Core causes it A LOT.