The new artist activity graph seems to show some artists as two separate entries. The individual counts are “correct” for entry, and sum up to the total count the artist should have.
See the following example from my last year stats:
The artist activity graph shows GFRIEND twice, once under their Latin name (GFRIEND), once with their Korean name (여자친구). I suspect this is because some of their release groups are credited to “GFRIEND”, others to “여자친구”.
However, the top artists stats correctly show just a single entry for them. Thus, the issue appears specific to this new graph.