Samsung is aware of this symptom which may appear on limited Galaxy S10 Series due to camera software issue and it can be occurred on specific video size when ultra wide camera is used.
If you record videos in the following conditions, “Enabled HDR 10+ and 16:9(HD resolution)/ Full size”, video can be recorded poor quality.
Regarding this problem, Samsung is scheduled to release a new software at earliest possible. Therefore please check regularly for updates to your device SW via the Smart Switch PC or FOTA.
Alternatively to proper use a ultra wide camera when recording the video before new S/W update, please disable HDR 10+ feature or select 1:1/ 16:9(FHD/UHD resolution) video size on camera settings.