Operating system: Windows-10-10.0.1709 64 Bits
Graphics card: GeForce GTX 1050 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 436.30
Broken: version: 2.81 (sub 13), branch: master, commit date: 2019-10-02 17:42, hash: rBaabd8701e985
Short description of error
If i assign materials to different Faces of a single Mesh they become transparent and switching slots order or pushing anyone up makes it transparent.
Exact steps for others to reproduce the error
Assign different Materials to Suzanne second one becomes transparent.
Switching the order will switch the one who becomes transparent and the more you add the whole Mesh gets affected.
[Based on the default startup or an attached .blend file (as simple as possible)]