There's a technical problem with your Android app. It's actually not a bug, but rather a mistake in its implementation.
In Android, you're able to set certain WiFi networks as "metered" or "restricted", so that apps that can do heavy downloads over unrestricted WiFi will not do so over these restricted WiFi networks. They are to be treated as being on the same level as a mobile data connection.
In fact, whenever a mobile hotspot network is used, Android automatically designates this network as "metered" or "restricted". Most well-designed apps respect this designation and will not do any heavy downloads. For example, Google Play Store will NOT update any apps while on a restricted WiFi network.
The thing I noticed about Spotify Android app is that it does not care at all whether the WiFi network is restricted. It downloads new songs in offline playlists anyway. This is in UTTER GROSS VIOLATION of user expectation that a restricted or metered WiFi network will be respected by all apps.
Please note that I have made sure that the setting "Download using cellular" has been switched off in my Spotify app, so that is not the issue. Also, this setting should actually be "Download using metered connections"