The correct answer from the @Fangjun Jiang：
“Can someone from the Mathworks give an explaination of this change on the Scope block? I've answered questions similar to this twice before. I think the "smartness" of the Scope block actually confused user.
In this extream simple example, in the Scope window, go to menu View, Style, you will see the "Marker" is set as "o". That is why. Usually, it is set as "none". But in this case, even if you set it as "none" and click "Apply", when you run simulation again, it will automatically go back to "o" and still show the same plot with just one dot.
It is the correct display, considering that the Scope is connected to the Constant block. But that is probabbly another lengthy discussion. If you want to show the "tradictional" view, you can change the sample time of the Constant block from "inf" to "-1", then you will see a horizontal line. You can further play with the setting on "Marker".
I think whatever the default behavior of the Scope with values of "inf" sample time is confusing users.”