As with any mouse, the optical sensor occasionally gets dirty. Where a roller mouse differs is how you get to the sensor. While they are fragile, when cleaned frequently these ergonomic pointer devices can truck along for years.
Proper cleaning steps: [manufacturer video]
1. Turn off keyboard and unplug
2. Remove both round clips by pushing inwards and rotating them upwards, outside edge goes upwards.
3. On one side there's a sensor connector, tilt the other side upwards
4. Pull the mouse 'tube' off gently.
5. Use canned air or blower to blow out the tube
6. Use canned air or blower to dust off mouse sensor and inner rail.
7. Reassemble in reverse order.