The caching mechanism (which is used to spread GetItemInfo calls over a longer period of time) seems to fail for a large number of entries, in Classic only. I didn't look into it, but at first glance the items being reported as failing are actually valid. They can be displayed in the UI and tooltip.

Example: The Heartbreaker is a toy that should exist. It shouldn't fail to load, nor does it (apparently). The DB exports it, as well.