This has happened to me twice. The first time I stumbled across the solution by starting over from scratch making a DLC and did not have a backup of the old YMT to compare with.
The first time it happened it was to a baseball cap that had a logo texture. The second time it happened to some glasses that have a glass/plastic layer.
This was the broken hat.
This was the working one. Both of them were the same model/texture combinations.
A more obvious one is this.
And here it is working. This is the same model after removing and recreating the prop eyes section.
According to this comparison of the XMLs from the broken (left) and working(right) YMT files, you can see the propid numbers being incorrect. I am not sure how this happened, because in the YMTEditor itself the eye section started at 0.
This has happened to me twice. The first time I stumbled across the solution by starting over from scratch making a DLC and did not have a backup of the old YMT to compare with. The first time it happened it was to a baseball cap that had a logo texture. The second time it happened to some glasses that have a glass/plastic layer. This was the broken hat. This was the working one. Both of them were the same model/texture combinations. A more obvious one is this. And here it is working. This is the same model after removing and recreating the prop eyes section. According to this comparison of the XMLs from the broken (left) and working(right) YMT files, you can see the propid numbers being incorrect. I am not sure how this happened, because in the YMTEditor itself the eye section started at 0.