How to reproduce:
1. Open the project "case_1216855-Fbx_Exporter"
2. Open the scene "SampleScene"
3. Select the GameObject "Sphere Emission Color" in the Hierarchy and notice that the Material "Emission Color" is applied
4. Right-click on the GameObject "Sphere Emission Color" in the Hierarchy
5. Select "Export To FBX..." in the Context Menu
6. Select "Export" in the Export Options window
7. Select the "Sphere Emission Color" in the Assets folder in the Project window
8. Observe the results in the Remapped Materials section in the Inspector

Expected results: the name of the Remapped Material is "Emission Color" is the same as the Material's "Emission Color"
Actual results: the name of the Remapped Material "Emission_Color" is not the same as the Material's name "Emission Color"

Reproducible with: 3.0.1-peview.2 (2018.4.16f1, 2019.3.1f1, 2020.1.0a24)
Could not test with: 2017.4.37f1 because FBX Exporter package is not supported

Notes:
1. It works fine when there aren't any spaces in a Material's name
2. There is an underscore in the Remapped Material's name instead of each space in the Material's name applied in the GameObject