delete file from ios

I ahve the same app and ios version and just tested a pdf of the root. it deletes as expected. Maybe try backing up the data and formatting the drive. if you have 32GB or less use FAT32 and if 64 or higher use exFAT for the files system. If you are using a mac to format the drive make sure and use MBR partition scheme. MAC defaults to GUID and that is not compatible with the app.