There are only 2 ways that a file would not show up in unrealBook after refreshing the list manually, either the file is not there or there is no .pdf or .PDF on the end of the filename. unrealBook does a query on all the files and then only shows .pdf or .PDF extension files along with misc. other files it needs.
On lists that don’t have a rebuild button, pull down on the list to refresh and rescan the files.
Pull down on a list to refresh.