Excel cannot handle paths or file names with square brackets in them, it is a documented limitation due to square brackets being used in formulas that refer to other workbooks. Using square brackets in filenames or paths causes problems with how Excelinterprets the path or filename.
https://community.box.com/t5/Archive-Forum/Box-Drive-Mac-Excel-Paths-with-Square-Brackets-Cannot-Access/td-p/63286
