Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 452.06
Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-09-09 00:05, hash: rBb8840c105a4e
Worked: (newest version of Blender that worked as expected)
Short description of error
obj file import automatically creates a second image texture node if the material has a .png file assigned, and then connects the colour output of the second image node into the principled's alpha input, needs to be the alpha output which connects to the principled alpha input.
Import file and examine material of imported object