Why material is at the end

There are several reasons, and only one of them means the tool did not cope.

• The file has no sound. A drone, an action camera with the microphone off, a camera set not to record sound. The tooltip says TAIL · no audio in this file.
• There is sound, but it is silence. A dead microphone, a forgotten level. The tooltip says TAIL · this file is silent.
• It is material of its own. B-roll, cutaways, pickups: shot on their own, with nobody else recording at that time. The tooltip says TAIL · nothing else was rolling at this time.
• We did not cope. There is sound, other devices were recording, and the clip is still at the end. That one is on us. Save a report through Export, then Something went wrong…, and send it to us. See Problem report.

On some shoots there is a lot of such material, and that is not a failed sync but a property of the shoot. So you do not have to hunt for those clips at the end, turn on Unplaced clips in shooting order, see Clips without proof.