Huawei originally advertised the Mate 9 with UHS 2.1 storage, but some units are purportedly shipping with the slower eMMC 5.1 standard without any official statements from the manufacturer. Furthermore, sources say some advertisements have been silently changed to reflect the switch to eMMC 5.1.
http://www.notebookcheck.net/Huawei-reportedly-shipping-Mate-9-and-P10-models-with-slower-eMMC-storage.214404.0.html
This is a disturbing trend. Dell's sourcing of Toshiba SSDs running at 1/3rd the speed of the Samsung SSDs (while sending most reviewers units with the faster SSDs) was not okay. This takes it to an even worse level.