When the Properties is showing a video capture, hit OK, then right-click the source in the Sources list. Go to Transforms, 'Reset Transform', then do the same and 'Fit to Screen'.
Sometimes the source can just be initialized off-screen sometimes.
Also, make sure you do NOT have two Video Capture Source sources pointed at the same capture card/webcam; if you want to use the same one in a different scene, use 'add existing', not 'add new'. Only one program can access most video cap devices at a time, and each VCD Source counts as a separate program.
If that doesn't work, please post a logfile from a live streaming or recording session at least 30 seconds in length where the issue is occurring.
