Currently the modpack uses inventory tweaks refoxed, I do not know if its a problem on my part or if this mod is intentionally barebones but it basically only adds inventory sorting and I would like to note that there are much better Inventory management mods available for example 

https://www.curseforge.com/minecraft/mc-mods/quark One of the most well known and customizable mods ever that also includes inventory shortcuts to sort item stacks from player inventory to existing stacks and many more small but potentially usefull changes which can all easily be toggled

or 

https://www.curseforge.com/minecraft/mc-mods/sophisticated-inventory-interactions A Mod that just adds all sophisticated Inventory buttons to all container inventories