It seems as though the Android app completely skips over certain files and file types. I have an internal /CallRecordings/ directory that has some .amr files in it, and when I backup 'Other Files' they get completely ignored. As a test I renamed one of the .amr files to .txt and it started to backup just fine.
When I navigate to the /CallRecordings/ directory through IDrive I can't even see the files, so the backup button is greyed out.
I also use a program called FolderSync that saves it's settings backup to /Android/data/dk.tacit.android.foldersync/files/backup/, however it seems as though the /Android/data/ folder gets completely ignored by IDrive. There are 3 folders in /Android/, data, media, and obb, but only media and obb get backed up.
As a test I tried changing where FolderSync saves its settings backup to the /Download/ folder, however it *still* didn't backup the FolderSync settings backup files, even though it does backup other files in the /Download/ folder.
It's pretty hard to trust backup software that just completely disregards certain files and file types.