I’ve not seen it happen with red but I have had an avatar before where the mobile shader made it appear green - I kept messing around in Unity but couldn’t figure it out. After a while I took a look at the model in blender and found out it had vertex paint on it, it seems the mobile shader takes the vertex paint from the FBX model and shows that through. If this is the cause for your red issue then you might want to check the model in Blender. (note that vertex paint is different to weight painting)