See picture below. (Sorry about the quality but the issue is still visible.)
The part is 6 mm and the hole is Ø3 mm which means there is 1.5 mm on each side of the hole that should be filled. Seems like it shouldn't be a problem but apparently it is. Extrusion width is 0.5 mm.
I'm guessing there should be a simple way to solve this issue but I haven't found it.
This part is not the first one I've had the same issue with. Holes being printed "stupidly", leaving gaps. Come to think of it, I have a photo of a different part with much bigger holes showing the same problem towards the part perimeter. See picture: