Hi I had the same problem about a month ago
Are you using the Modes app , do not disturb/ work / relax etc etc
Turn those off and also try updating any apps one by one via the Samsung Galaxy Store by going to your installed apps lists and checking one by one. This resolved my issue straight away, I can't be definite but it definitely worked for me .... if that doesn't work then a full system reset is the next option but ensure you back up ALL your data via Google dack up and sign out of your Google and Samsung account Smart Switch as you will loose ALL your data including pictures and music saved on your device. I advice you remove any memory cards from your device before you do this.
Hope this helps. Let us know
Best wishes

