Text or imessage sound notification not working...

My phone is not waking-up and making a sound notification when I receive a text message or an imessage. I opened a case with Apple, spoke to 3 different agents made me check all the parameter and everything was fine. I ended-up having to erase the phone, re-downloaded IOS 11.2 and restored with a back-up in Itune including 60-70 apps (lost my apple watch activity datas).

Still not working !! Does not seem to be hardware as the notification works when the phone is alive. Facetime notification and normal calls are working. Bit tired of spending hours with first line agent that are good with the basic but can't solve the issue. Anyone had that problem and came-up with a fix??

Thanks

rdquebec