Still having severe lag issues. After a couple of minutes, the game just freezes for 5-10 seconds every 30 seconds or so, and CPU fan runs at high speed during the freezes. Seems the game now requires more than 12Gb of RAM, which I cannot provide because my machine only has 16Gb. I saw forum posts recommending 6Gb, I bumped it up to 8Gb, then to 12Gb, seems this is never enough. Besides of the lag, the game constantly crashes or hangs, requiring full restart. Modded Minecraft is now insanely frustrating, requiring regular full restart from scratch on different modpacks. I have major difficulties mining, it takes me hours and hours and hours to get a couple of pieces of iron, so I focused on skyblock packs, but now the current skyblock pack requires 32Gb of RAM, which is in my opinion a real non-sense. If packs are so unstable, I really need a way to transfer my world from one pack to another, but each time I searched for this, it was impossible. Of course, some parts of my world would be broken if they rely on mods absent from the new packs, but at least the collected resources and infrastructures based on mods present in the new pack would be preserved. I don't care anymore about packs with progression. I now know these are just non-sense, if the game is too unstable to run a lot of mods. This will just lead to dead ends requiring intense cheating and need to abort playback and start from scratch on another world, another pack.
Besides constant need to restart the pack, alt-tabbing out of Minecraft now takes several seconds, for no reason, and JEI causes some parts of the inventory GUI to be inaccessible in GUI scale auto (e.g., the + sign in the crafting recipe).
Is there any way to speed up loading of the pack? Again, seems I need to upgrade my PC with a RAID setup to have it load faster.
Yes, I can to downgrade from 3.4 to 3.3, because the issues started with the 3.4 version that added Thaumcraft, but I don't want to get Endermen Evolution back and I suspect downgrading will completely break the questbook.