Is this still being maintained?
There's an actual bug with the Beelzebub, Ultimate Ifrit, and Ultimate Beelzebub Neck part. Some of the entries seem to conflate the parts that drop from the front and the back of the neck, so you can have a bunch of, say, Ulti Ifrit's Necks in your inventory, but when synthing a sword that requires said part, it will say you have 0 because it thinks you have the other part.
The original Ifrit is working properly, with the front and back parts labelled as Head and Neck separately. Just the others that are bugged.