Although it might not affect all Dell XPS 15 9575 units that were patched with the latest BIOS update, it seems that at least some of this convertible's users are now facing a buggy trackpad. For now, the problem is being investigated by Dell's engineers, so a solution should surface as soon as possible.
https://www.notebookcheck.net/Latest-Dell-XPS-15-9575-BIOS-update-comes-with-a-trackpad-bug.321180.0.html