After the update of PAE2 fuild interfaces can be equiped two capacity card, which means up to 6 upgrade slots are needed in dual interface.
So in order to equip those upgrades, two more extra slots are needed.

well it seems bit troublesome to deal with. i can't promise when i can fix it

fixed in https://github.com/GlodBlock/AE2FluidCraft-Rework/releases/tag/2.4.12-r