My Box search index is wrong

I have realised that the Box search index for my 25Gb of files on Box is wrong, or at least incomplete. When I search (by filename, I'm not talking about the content of the files) for files that I know are on Box  - I can see them via the file structure on Box both online and in my Box Drive folder on Windows - the search comes back with "There are no items matching your query" - even when I'm looking at the file in the folder. I know there can sometimes be a delay in indexing files, but most of these files have been on Box for months if not years. How do I get Box to index them properly? I've found hundreds of examples of files that don't come up in the search now I'm looking for them, and I need to get the index fixed. Please advise