Have you assigned your machine/product to the correct prekit group? Some machines or products may be set to prekit by the case and will only call for product in prekitting if the quantity needed is at least a full case.
Also, if your parlevel is set low for certain slots, you may want to prekit by the unit instead of by the case. If a product has not fallen below the set parlevel, it will not be called for in prekitting, so be sure to check what your current parlevel is for affected slots and compare to the prekit group or product settings.
Machine and product prekit settings are now configured via the prekit group that they belong to, found under Settings > Warehouse > Prekit Groups, as well as the product's individual settings in the Product Catalog.