I'd like to bump this topic. I'm having the same issue with an Ender 5 Plus. It's small gaps at the seam of a perimeter, but it's not a Z seam. For my object, which is very similar in shape to yours, it draws the perimeters from inside to outside, then after completing the outer most perimeter, it crosses back to the middle to do the infill. It's like there is coasting or something turned on, but it's not. Very frustrating and I have not been able to figure out a solution. Most people seem to have a bulge at the seam, I have a dip.