The 256k Item Storage Part's crafting recipe requires the highest tier of Fluid Storage Part in base Refined Storage.

Also, just a suggestion, but configuration to disable the extra storage disks would be nice.

Found your problem:
https://github.com/TechReborn/RebornStorage/blob/1.12/src/main/java/RebornStorage/init/ModRecipes.java#L57
That's the recipe for the first tier of Fluid Storage Part... but it's specifying that the output is an Item Storage Part!