I have the same issue with my Samsung Galaxy Note 4. This problem surfaced after I upgraded to Android 5 from Android 4.x . I read that clearing the cache can help. But I've seen situations where it helps for a while then starts reoccurring. Most recently I updated to the latest Android 5.1.1but the problem persists. I have no other Bluetooth issues with my phone or any other devices. This certainly has become an annoyance and hopefully Lexus IS looking into the reasons for this.