System Information
Operating system: Windows 7 Pro, x64
Graphics card:
Blender Version
Broken: blender-2.82a-windows64
Worked: blender-2.80rc3-windows64
When you assign a second material to a single object, the polygons that the second material is assigned to become transparent. In the version of blender-2. 80rc3-windows64, this problem is not observed. I attach a file that demonstrates this problem.