Spotify Does Not Play Songs on My Windows Mobile 10 Lumias

[Triakel]

Hello. I need help resolving an issue with Spotify on both my Lumia Icon (930) and my Lumia 735. 

At the end of this month, Microsoft is shutting down streaming functionality for its Groove Music apps. Users are being encouraged to migrate to Spotify, which is described as a "partner" in this transition. I am both a Spotify Premium and Groove Music Pass subscriber, so I had hopes this transition would be smooth for me.

Unfortunately, I am unable to play any songs in Spotify, either streamed or downloaded as "offline" tracks on either phone. The app loads, looks normal, is navigable ... it just doesn't play anything (or if it does, it will play a half-second of music and then stop). 

I've tried rebooting both phones, as well as uninstalling and reinstalling the Spotify app. I even reset my Lumia Icon in hopes that would help. Nope.

Groove has always worked just fine on both phones. I can also stream content through the Edge browser (YouTube, Soundcloud, Bandcamp, etc.). But Spotify does not work. 

Since I am a paying subscriber on an ostensibly still-supported "partner" platform, I am requesting instructions how to enable Spotify functionality on my phone. I suspect a software update is needed to address Spotify streaming issues on these phones.

Thank you.