I have Spotify installed on an iPhone 3GS (part of an entertainment center) and my iPhone 6 (my daily-use mobile).  When I have the app running on both and select the iPhone 3GS in Connect on the iPhone 6, the iPhone 6 screen goes blank and I lose control of the app.  Whatever queue was playing continues to play, but I can no longer control the app on the iPhone 6.  The app's screen remains blank, and the lock screen transport controls also do not work.

The issue is not consistent; occasionally, everything works normally.  I have not been able to identify any controlling circumstances between the two behaviors.

For some reason, when I select "Report an Issue/Bug" on the official Spotify help page, I'm never given an opportunity to actually report anything...

Here's info about the iPhone 6 environment when the issue occurs:

iPhone model: ME344LL/A

iOS version: 8.4.1 (12H321)

Carrier: Verizon 20.0

Spotify version: 3.8.0

Using WiFi: Yes

I'll come back with more info about the 3GS environment when I get home.