A similar incident like this happened a few days ago where we learnt that Google Pixel 2 phones are facing a problem where the microphone stops working. Many users tweeted about their difficulty, but they found out a way to make it work. It happened to them while they were on a call, or using the Google Assistant app. They blew air into the microphone which helped them get back the sound. Peculiar as this is Galaxy S8 and S8 + flagship is also facing the similar crisis.
As you can see users have briefly explained the issue they faced. You can see users of Note 8, S8 and S8+ are complaining about the mic not working. This happens during a call or while using assistant apps. After the issue was faced by the users they tried to blow air into the microphone and though it’s hilarious the problem was solved.
This is not the permanent solution but at least as of now, it is working for many users. Samsung also like Google has not yet commented on anything about this issue.