I've tried all basic troubleshooting & the native messaging app will not notify with sound on my S20, only edge lighting... 3rd party apps from the play store will notify with sound yet no edge lighting... Had anyone had an issue like this? It's there a underlying issue to why one works yet the other not? Anything? Anyone?
Are you using the native messaging app when you are experiencing no notification sound?
When you go to the messaging app > tap on the 3 dots on the right side > tap on settings > tap on notifications > tap on new messages > what is your notification style set to?