DIAGNOSIS Adhesive residue from the tape backing has built up on the cutter blade, causing a dull, sticky edge.
FIX Power off the P21. Manually open the cutter cover. Apply a drop of >90% isopropyl alcohol directly onto the stainless steel blade edge. Operate the cutting lever 10-15 times to work the alcohol through the mechanism. This dissolves the adhesive. Wipe away any black residue from the blade and the plastic slot with a lint-free cloth. Let it dry for 1 minute. Test with a print.
IF THAT DIDN'T WORK The blade may be dull from cutting non-standard materials (e.g., laminated stickers). The P21 cutter is designed for standard thermal label tape only. Blade replacement is not a user-serviceable part.
HEADS UP Do not use oil, WD-40, or water to clean the cutter. This will attract more debris and gum up the mechanism permanently. Never use abrasive tools like sandpaper or a file on the blade.