I also have the Stick+ and have had the same thing happen to me. I have a Sony XBR 900E television that has 4 HDMI ports that all support HDCP 2.2. I tried a couple of different ports and also a new Stick+ (returned the old one) to no avail. Happens about 2 times a week. A restart of the Roku fixes it until next time.
Personally, I'm convinced that it's a Roku firmware or hardware issue. Most of the other people reporting this issue have a Roku device that is connected via a HDMI cable and apparently changing cables fixes it for them. For us, since there is no cable involved, I think we are just stuck with it until Roku fixes the problem.
I mostly use the Roku Stick+ rather than the Sony's built-in apps. I find the Roku interface much more responsive than the Sony Android one. Additionally, since I tend to watch FoxNews during the day, the app on the Roku is not as, shall I say, "buggy" as the one on Android. The Android one continues to broadcast the audio even after exiting out of the app - no such problem on the Roku.