Occasional irregular lines / banding

Hi

My printer has been working fine for ages, however my taller prints rare now getting these irregular lines / bands

Attachment 6638

Any idea what could be causing the issue ?

Have you ever replaced your nozzle? Cleaned your nozzle? How long have you been printing with this nozzle? Have you changed brands of filament recently? Have you fine tuned your extrusion multiplier recently?

What kind of printer do you have? It could be wear on the bearings, wear on threaded rods or nuts (they can wear and get loose over time). It's easier to diagnose if we know what you have.