Using Outlook for Android in business environments for email and scheduling
Definitely not just Chinese phones. I have a Moto G4 Plus and I'm having the same issue, as of the update that just downloaded today, which is 3.0.107.
Same issue here and I'm using a Pixel 3XL. It's a bug and it resurfaces time and time again. Trying to explain this to the people in the support chat in the app is pretty useless too, as they default to canned responses as IF it's an account problem.
The recommendation to wipe the app and re-add accounts is insane. I won't keeping wiping my mail app and setting up multiple accounts for something like this. Oddly enough, I have no issues with the app's outgoing mail sound. It's almost as if the update didn't include the new mail sound or some section of the code lost the pointer to it.
It's a RECURRING PROBLEM MICROSOFT, FIX IT once and for all.