All Android devices with SD card slots and support for expanded storage formatting. (In my specific case, an Amazon Kindle Fire HD 8 2018)
Android 9 (probably also present on Android 7, 8, 10 & 11 as the SD card handling remained the same since 6)
My Question or Issue
When using an SD card setup in Android "expanded storage" mode (the internal storage gets remapped to the SD card), Spotify downloads get stored on the SD card, which is the expected behavior.
However, when the SD card is disconnected, for example during every reboot, the Spotify app instantly starts to download all songs again to the internal storage, which is very annoying to say the least, especially when your device is almost full anyways. Even worse is the fact, that there is no way to delete these new downloads, without also deleting the downloads on the SD card and all other app data. So basically, if I reboot my device, I have to reinstall Spotify and start downloading everything again, which renders the download function entirely useless.
I'd suggest having the app wait for the system wide storage device check after boot, or maybe lowering the auto-start priority (after all, Spotify is by no means and essential app that needs to run immediately). This way, the app wouldn't even notice, that the downloads weren't available for a couple of seconds and normal behavior could be restored.