The opening of the blade is obstructed (with built up materials). Cutting efforts appear to not fully cut through (even in using the proper settings), or appear to give a clean cut in some areas but not others. In some rare cases, the concern causes a cutting misalignment.
During the cutting process, some materials that are fibrous in nature (such as paper and cardstock) may collect fiber strands or pulp as the blade cuts through them. This can build up over time within the aperture of where the blade protrudes.
Grip the tip of the blade and unscrew it. Any debris that has built up can then be cleaned out. When finished, screw the tip back into place.
NOTE: You should never cut with the tip removed.
With some older blade models where the tip cannot be unscrewed, the blade may alternately be exposed to a level of 10. A fine tipped brush (such as a soft paint brush with bristles that have fine tips) or other fine tipped tool may then be used to attempt to dislodge the material. You can blow into the aperture to remove this material once it has become dislodged.