@yukinoh1989 I’m not expert but if I remember correctly this is sometimes caused by either the resolution of the image texture being too low or the UV islands being too far apart. Maybe try rearranging your image texture a bit? Assuming that you’re trying to paint on two islands at once that is.
Actually (didn’t want to delete what I wrote because it may be helpful to others) is your model consisting exclusively of triangles? If so I’m assuming you haven’t retopologized it, and in that case that could be the cause (again though, not an expert, but retopo-ing your sculpts is usually good practice anyways).
