Occasional failure to close workbook

[mnich0ls]

Hi @damuellen, I'm occasionally seeing a fatalException when attempting to close a workbook with the error message "Error creating output xlsx file. Usually a permissions error." - I have not been able to reproduce this on my own hardware, but we're seeing it on some iOS devices in field testing. This is only happening occasionally though. The file names we give our workbooks use a timestamp convention, there is no user-defined text used in the file name. Do you have any suggestions on how I can debug this?