Hi John,
What happens if you Solo Track 3? (Click the “!” in the tracker header)
If you don’t see that event in the preview window when your cursor is somewhere in that event then something is wrong.
Following up on Wayne and Graham’s thoughts, let’s look closer at the video event on Track 3. Click on the Video Event on Track 3. Right Click -> Switches. Is ‘Mute’ checked?

If so, it will not show. When I mute an event, it turns gray like your picture.
There are many different ways to achieve the same results and all of us have our own workflow techniques, but based on your initial description, may I suggest a change in your workflow?
Instead of messing with Composite envelopes to cut between the two Video tracks, why not split/cut the upper video event to reveal the lower? Cutting events are non-destructive to the media file.
If I have 2 cameras and I want to cut between them, I go to the frame I want to make the change. Select the top Video event (you should see it in the preview), hit the ‘S’ key to split the event. Vegas automatically selects the event to the right of the split. Then I ‘Mute’ the rest of the event on that track. Notice I have the Event ‘Mute’ function mapped to the ‘Alt+M’ hotkey in my picture above?
Then I scrub through the video (the lower video event is now showing in the preview) and when I get to the frame where I want to switch back to the top-level video event, I hit the ‘S’ key again to split the event, “ALT+M” will ‘un-Mute’ the muted event. Now the top video track event is showing again.
And if instead of a hard cut, you want to do a fade – simply apply grab the small triangle in the top left of the event and drag to the right to make a fade in.
Happy editing.
Regards,
–Doug
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