If you are using Serato Video with the Pioneer DDJ-SX2 you might notice your hardware crossfader sending some whacky signals to the linked Serato Video crossfader. We were able to determine this was an issue caused by a utility setting of the DDJ-SX2.
You can resolve this issue by disabling the "Optimization of Crossfader midi messages" feature which is done by putting the DDJ-SX2 into Utility Settings mode, and turning the feature off.
Steps on how to do this, along with other utility settings for the controller are documented in the DDJ-SX2 user manual from Pioneer's website;
Please consult the support team if you are having any further issues.