I think that the fact that it worked before was just pure luck. If a model has no skin, its transparency is taken from the material setting. In older A7 versions that did not expect models without skin, the transparency was undetermined in such a case.

The solution is to use a transparent texture with alpha channel for the transparent part, and a not transparent texture for the nontransparent part. This causes the model to be rendered twice, which is necessary when it has both transparent and nontransparent parts.