I've been making my way through the batch of newly released videos by NIST and I thought these were quite interesting. They show multiple 'ejections' (for lack of a better word) from the WTC North Tower with a white trail of smoke burning behind them. Contrast these ejections with multiple other objects and debris falling from the tower that do not have any smoke trails, suggesting that there is something different about the 'white trail' objects. One hypothesis: We know that smoke from thermitic reactions burns white, and we know (e.g., Harrit, Jones, et al.) that thermite is prevalent in the dust from the collapses. Perhaps that's what you're seeing in this video.

In the second clip ("NY1 6 Raw 10"), pay attention to the first ejection, which falls at :32 into the video. It seems that there is no white smoke at first, but that as it's falling, the smoke starts. Perhaps a delayed thermitic reaction? Then you see more of the same on the right side of the video.