It looks like there's a bug with the latest version of the Spotify Music app on iOS, which appears to let the app absolutely scream through your mobile data quota — even if you're playing already-downloaded music. Until a fix is delivered, we'd strongly recommend you disable mobile data in your iPhone's settings.
We've been seeing more than one or two reports of this happening over the last few days:
— Stephen (@mrgrumpystephen) April 18, 2016
@SpotifyCares new iOS updateeven when playing dwnloaded tracks - used 5gb of mobile data in two days! what is going on, absolutely fuming
— Tom George (@tomknexmaster) April 19, 2016
This is apparently happening even with Spotify's default "download over cellular" option within the app disabled, as it is by default.
A couple of readers have told us that they've seen excessively large data usage — in the order of a couple of gigabytes or more — even while they've been listening on Wi-Fi, and to music previously synced to play offline on iPhones (and cellular-enabled iPads). These kinds of reports are always hard to verify, but we're erring on the side of caution seeing how expensive excess mobile data is in Australia.
We've contacted Spotify to see if it's a widespread issue, and if there are any plans for an update to the app in the near future to sort this out. At the very least, it's worth diving into your iPhone's settings to check how much data the app is using. To do that, hit Settings, then Mobile, then scroll down to the list of apps and check the data usage figure next to Spotify.
If the figure you're seeing is unreasonably large, then the app might be bugging out on you too. There's a easy fix for this in the interim — stop the Spotify Music app from accessing any mobile data at all. To do that, go into Settings, then Mobile, then scroll down to the list of apps allowed to use mobile data, and tap the radio button next to the Spotify Music app.
FYI if you use Spotify for offline music might wanna flick off mobile data as current version monsters your data pic.twitter.com/MVlzVc39id
— Stephen (@mrgrumpystephen) April 19, 2016
(Cheers to Stephen on Twitter for the initial heads-up!)