1. Have you tried manually quitting the camera app and also both restarting and force restarting your iPhone?
On iPhone, try quitting and reopening an app if it isn’t responding.
support.apple.com
Learn how to turn your iPhone off, then back on.
support.apple.com
If iPhone isn’t responding, try forcing it to restart.
support.apple.com
2. When the frame freezes, does the video duration counter at the top also freeze or does it continue counting?
3. When you go to view the video, did you discover that the frame was frozen in the actual video as well, or was the camera still recording what you were pointing it at (but just not showing it "live")?