Certain items not coming up when searching by keyword

I have generally had no issues searching by keyword to bring up titles of items that I am looking for, but there’s a handful of items in my collection that for some reason will not show up when I search this way. These items DO come up when I use exact match or advanced search, so I am able to find them through those options, but it seems very strange that they can’t be found through keywords when all other items in the collection can. Could there be a common problem among these items causing this to happen / making them not searchable? Has anyone else experienced anything like this?

What are some examples of the things that don’t work in the search?

The basic “fulltext” search has some restrictions: the ones people run up against are usually that short words are ignored, and that words that appear in over half of your records are also ignored.