If I disregard the sentence that it was not yet visible at the beginning, I would assume that the scaffolding layer was exactly in that area. And then it would just be a plaster start, because it was not worked fresh on fresh. It can also be worked too thin in the reinforcement layer, making the overlap of the fabric visible. Furthermore, due to the aforementioned issue, a structural difference can also arise if a part of the mortar is worked too late, caused by the change in the scaffolding layer during application and scraping. It is always difficult to assess from the photo. Theoretically, re-plastering is possible, but then it must be worked in two layers again and fully over the surface. Partial is not possible, that would look worse than now.