I notice that when I have my Note 9's camera resolution set to QHD, 60 fps (the highest), when the camera app comes up and I see the video on the screen, ready to record, there's about a 3 second pause (the entire screen freezes as if it's too much to handle), then the video resumes, and this happens every 6 seconds or so. Every 6 seconds, the video would just pause for a few seconds like it's trying to catch up. When I record using QHD, I notice the same behavior when playing the video back. The video stammers, but the audio continues seamlessly. When I switch to a lesser resolution, the problem mostly is resolved. What can I do to fix this?
It seems that clearing G camera cache can help temporarily. It seems to be phone issue and I would suggest that you should raise this issue in Samsung forum or seek help from Samsung service center.
Quoted from the link above
Dear trebills and others in this thread, This is Cole from Samsung Electronics’ North American offices. We would like to further discuss this issue with you. Would you be willing to provide your contact information in a private message so that one of our technical support agents can get more detailed information about your difficulty?
Thus best way would be to contact Samsung support. It seems they are also trying to debug the issue.