iSNAFU.
Sometimes when people have reported this issue in the forums, some replies have been able to find the file and others haven't.
In my case, with dozens, maybe hundreds, of files, the main keywords were 'disappeared' presumably during the ESP process. In some of these, I could find them when searching within my own port but not within the whole collection with the same search.

Which would be highly-unlikely-to-impossible outwith iS.