Hey @userUhIENw1QPY, I hope you're doing well.
Is this happening in any vehicle or is it specific to certain vehicles you frequently ride in or are connected to via bluetooth?
It can be anything but I am wondering if you are connecting to bluetooth and Bixby Routines is running and automatically running a routine to Silence/Mute your phone. To check if you have any active routines, open the Bixby Routines app. If you have any that look like they might relate to car rides or media, check them out and maybe disable them and test your sound in a vehicle.
I'll wait to hear back from you.
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I have the same issue. Notification sounds stop when in the car and connected via bluetooth. Bixby is not set up for any routines. Notification sounds return once bluetooth disconnects from the car.