Thank you so much for your feedback!
No, it's not a known issue. Do you play videos from Quest local storage, or stream videos from your computer to headset via SMB, DLNA or AirScreen?
Can you tell us the previous filename and the current filename of your 200-degree video? In other words, the sound plays normally in what VR mode?
At present, we haven't reproduced the same issue. We'd much appreciate it if you can share with us a sample video for testing purpose. You can just tell us a download link(website) of the video or transfer the video through Google drive, One Drive, or torrent links.
Looking forward to your reply. We'll try fixing the issue once figuring out what went wrong.