When configuring the slots for Wither builder, there are weirdly two slot groups for soul sand, one for the top three soul sand and one for the bottom soul sand. If you configure the sides, the configuration copies between the slot groups. This is already strange, but also the bottom slot doesn't act like it's configured. This means if you try to pull from a chest, the bottom slot is left empty. If you disable the slots, the bottom slot still gets filled with soul sand from a hopper.

Industrial Foregoing Version:
1.16.5-3.2.14.6-14

Titanium Version:
1.16.5-3.2.8.4-10