Dean Drive Effects
One possible explanation for the thrust effect measured in the EmDrive a combination of vibrations, friction, and resonance with the attached measuring equipment causing apparent motion in the device. This effect is commonly referred to as the Dean Drive Effect, after a supposed reactionless drive invented by Norman Dean in the 1950's. It was eventually determined that the Dean Drive's apparent motion resulted from a combination of friction and vibrational effects, all of which depended on the experimental setup and meant the drive would be useless as a space drive (since there would be no surface against which friction could occur).
Unlike the Dean Drive, whose function was kept secret by its creator, the EmDrive has been independently tested in various orientations and experimental setups. It is unlikely that Dean Drive effects could account for the thrust measured across all these tests. Ultimately, the question of whether thrust is in part created by Dean Drive effects would be conclusively answered by a space test.