A Strange Bug in Private External Storage on Saucelabs: Error on Tab S7/S8 Devices but Not on Personal Devices

Question

I have a very strange bug with private external storage on tests run only on Saucelabs. It doesn't happen on real devices.

This works:

        val externalStorageVolumes: Array<out File> = ContextCompat.getExternalFilesDirs(applicationContext, "documents")

        val documents = externalStorageVolumes[0]

        val fileFolder = File(documents, "file")

        val fileFolderResult = fileFolder.mkdirs()

This doesn't work:

val documents = File(applicationContext.getExternalFilesDir(null), "documents")
val documentsMkdirResult = documents.mkdirs()

val fileFolder = File(documents, "file")
val fileFolderResult = fileFolder.mkdirs()

Only on their Tab S7/S8 devices and not on my Tab S7/S8, I get this error:

Primary directory null not allowed for content://media/external_primary/file; allowed directories are [Download, Documents]

but nothing in the official documentation seems to correlate the warning to the code:

https://developer.android.com/training/data-storage/app-specific#kotlin