Bluetooth

Your iPX uses a new BT chip 5.0 (different from the one intalled on your iP6s).

So you need to unpair and pair again your Bose speaker.

Pair a third-party Bluetooth accessory with your iPhone, iPad, or iPod touch - Apple Support

If this support article does not help you, try to contact the Bose support team and check if they have a new firmware update for your speaker model.

Regards

Giulio

I'd do a factory reset and before restoring any type of backup I would try to pair items and make sure they work. If you then restore and start having a problem again then you know it's an issue with the backup and not with the phone. If you have problems after setting it up as a new phone then I would take the phone in for a diagnostic test at an Apple Store.

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

I came to these forums to specifically search for this issue. It's happening to me with EVERYTHING on my iPhoneX. Even with airpods.... it says I'm connected to them and sound should be coming out but it only comes out of my phone. Requires restart. Can't figure out how to fix this. Imagine its a software or hardware issue as I've never had problems even remotely close to this. Also happening on my wife's phone with her X.