Looks like under extrusion to me.
You should inspect your filament diameter along the hole spool ( wind it on a temporary spool )
Thinner portions will have a double effect on the printed part: The extruder slips easier and the part gets less material.
Another cause could be a dropping hotend temperature for some reason. But I canĀ“t make up any scenery where this would happen and cure itself.
-Olaf