Some of Wacom's Pro Pens are so sensitive, Wacom by default configures pen pressure curve in the driver to have a small "deadzone" at the lowe end of pressure. This means the very lowest pressure readings are ignored.
Here is a screenshot showing that pressure deadzone in the default pressure curve the Wacom driver uses for the Wacom Pro Pen 2 (KP-504E)
Resources
Devid Revoy - Calibrating stylus pressure (for Krita) https://www.davidrevoy.com/article182/calibrating-wacom-stylus-pressure-on-krita