I upgraded my C5 pro to oreo recently, ever since I have had an issue with the notifications volume going back to near the middle of the bar even when I set it on mute. I set it manually to zero several times and everytime it goes back to the same spot near the middle of the bar.
The volume bars for other sounds (call, media) automatically slide to the corrosponding setting depending on the sound mode but the notifications one doesn't seem to follow.
The app in question is Medisafe, an app to remind me to take my daily pills in the morning and in the evening. I don't think it's due to the app.
I've also had issues with viber not always showing notifcations on the slide down menu but that's a separate thing.