Quality issue on PLA and P1P

When I print a 3dbenchy presliced on my P1P, each time it does about 20 layers flawlessly.
Then it makes a kind of scratching noise and proceeds to change color by a small bit, and print with lower quality.
See picture below

Any help is appreciated, Alex

This is the classic “Benchy hull line” issue and is caused by the print reaching the deck level and no longer doing infill, so it prints faster. With some filaments, especially silk PLA, this will change the appearance.