I am stuck with yet another issue. When I launch my world, it takes more than 45 seconds (after more than 5 minutes to start the pack), and then I get "shutting down the internal server" and the game crashes. This is really annoying, because I searched and cannot find any way to speed up the start of the game. The crash log has no useful information, except there was yet another ConcurentModificationException because of silly Java iterators not allowing to modify the iterated over collections and all mods doing all sorts of stuff concurrently. This worked in the past, I didn't update the pack nor the JVM, and then I cannot start my world anymore. I cannot continue playing that game if I have a limited time to complete packs, and then they go out of life and cannot start at all after a while.
In case this can help, here is the crash report: https://pastebin.com/X378WnnT.
Right before my game became unusable, starting to crash at world load, I was in the Aether trying to get the entrance to the Slider's Labyrinth. I searched for that totem for more than 3 hours without any result. Seems since the update to 3.6.0, something changed and the totem isn't generated anymore. I saw Direwolf20 find this entrance and defeat both the Slider and the Valkirie queen, but I'm stuck. Is it because packs now have a limited time duration and after a while, things break and we have to switch pack. That pretty much irons out non-kithensink packs for me then because I am working full time and can just play during weekends.