Material buildup. Your whole print is 20mm high except for in one corner of the print, where it seems that the nozzle is laying down extra material with each pass.

Chances are, it’s probably not. Most likely it is cooling, or lack of cooling actually. When your fan starts going out it doesn’t provide enough airflow to the part to cool it adequately. Then you get buildup in the areas of the part that are the most affected.