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Hard to tell just what you have there, but it appears that audio will be heard from tracks 1 and 2 - with some track 2 breaks - through where the video thumbnails end - then new audio on track 1 carries on without video. If you don't want those track 2 holes, close them up. Right-click in the gap and CLOSE GAP.
If you'd like someone to check out the problem, here's how...
1. Save your project. Then, with the entire project on the timeline, click the FILE menu. SAVE PORTABLE PROJECT AS. Save to any convenient folder.
2. Open the folder that contains the saved files and ZIP them all.
3. Upload the zip file to DropBox, Google Drive, MS OneDrive or the like. It's free.
4. Make the uploaded file public (share it) and copy the shared link.
5. Paste the link into this forum.