Bluetooth headphones controls problem after Android 7.1.1 Nougat update (Galaxy J5 2016)
A lot of this depends on:
1. How good the music app you are using is programmed.
2. Which KeyEvents your Bluetooth headset sends and how your app handles them.
I guess your headset uses same button for play/pause so there might not be proper handling of KeyEvents on the app side.
The solution is to try different app for music playback, check if YouTube app is working OK with your headset.
I will suggest you to use Google Play Music, as it works great with my Bluetooth headset with single play/pause button, running on Moto G4 Play (Android version 7.1.1).