Use the USB-Mux in a clean working environment.
Don't let the USB-Mux get in contact with water or coffee.
Make sure, that the USB-Mux does not damage your embedded device. The USB-Mux may, in certain modes of operation, back-power the DUT via the USB supply lines or may create connections on the data-lines that were not intended in the DUT's design.
Make sure that conditions, which the DUT is not designed to handle, are prevented.
While not actively tested in the development of the product, contact with other beverages than the ones listed above may also cause adverse effects.