Top row: (a) three-color composite image of the full 200 mas region for the image reconstruction from the April 2019 data, shown as a typical example. Here, Sgr A* (located at the image center) and S2 are color-coded in green, other potential targets are shown in red, and the residual map is shown in blue. The central white box indicates the central 100 mas region shown in other panels. (b) Stacking of the central 100 mas region around Sgr A* for April, June, July, August, and September 2019. The central bright spot at [0, 0] mas is Sgr A*, with its flux reduced 40 times. (c) Image from each month is shown in a different color, illustrating the motion in the south-east direction. Bottom row: three-color composite images of the central 100 mas region around Sgr A* for April, June, July, August, and September in 2019. In each map, Sgr A* is color-coded in green, other potential targets are shown in red, and the residual map is shown in blue. North is up and east to the left. S2 is outside of this region. We highlight the newly detected object with a white circle.