I created a new place, objSample.rbxl.
It just has the base plate and a single cube.
The cube has marble material, teal color, and two decals: crossed swords and a lightsaber.
I exported the cube as an obj file, which generated the following files:
GraniteCubeWithDecals.mtl
GraniteCubeWithDecals.obj
Part2Tex.png
Part3Tex.png
The png files look correct: crossed swords and light saber.
When I import the obj file in blender, I see a cube with the two decals on it.
Please try again on your end with the latest version of Studio.
If you see a problem, please reply with a post where you share the .rbxl file you’re using, and very specific instructions about which object(s) you are trying to export, what you expect to see as a result, and where things deviate from those expectations.