There are instances where some texture files cannot be exported from the editor. In this older post a user had reported this with the file T_Sky_Blue from the engine folder. Only this file has been reported that is included with the editor. Another user (TheJamsh) reported having an issue with one of his textures, but no follow up information.
1. Open UE4
2. Enable the view of the engine folder
3. Search the engine folder for T_Sky_Blue
4. Right Click and export the file to TGA or any other format
5. The file will not export (test with any other texture file if needed)
Expected: The file will export to it's original texture format or selected file type from the drop down menu
Results: Nothing is produced or saved to the folder location when the export happens.
Newly Added Repro
1. Grab files from //depot/UE4-UserContent/4.15/AssetPacks/SovietRoom415/Content/SovietRoom
2. Add them to New or Current project's content folder.
3. Locate 'Chandelier04_m'
4. Right-click > Asset Actions > Export.
Expected Exports as .TGA or another appropriate format.
Outcome Exports as a T3D object type.
Head over to the existingAnswerHub thread and let us know what's up.