Poor wideband MOS results can be the result of recording narrowband content (speech sample) in wideband format. This can be confirmed using the freeware Audacity tool:
This sample was recorded in narrowband format with narrowband content:
This sample was recorded in wideband format with wideband content:
This sample was recorded in wideband format with narrowband content. This sample exhibited poor MOS due to the fact that the recording format did not support the test content.