When I open a model (link) in the PlayCanvas Viewer that scales the root node along the X-axis by using the scale property it's displayed correctly:

When I modify the model (link) to use the matrix property instead of scale, the entire model is flipped along the vertical axis:

Both models validate without errors and are displayed correctly in almost every other viewer I tested (only Cesium had trouble with the normals, but this is a known issue).