When adding the SlotManagerComponent to any prefab and attempting to add a new slot to it, it defaults as EntitySlotInfo and does not allow the ability to change the slot class.
Basically, can't change the slot to RegisteringComponentSlotInfo or any other class type besides EntitySlotInfo.
Current workaround is to go into the text file of the prefab and change the slot type to whichever type is needed, then reload World Editor