The reason is that Line 3 and Line 6, which will be opened next year, have changed, but with the continuous planning of Beijing subway lines, the direction of Line 6 has changed, resulting in the merger of part of the originally planned Line 3 with the current Line 6 (that is, becoming a part of the current Line 6)! Therefore, the planning of Line 3 will be restarted, and some of them are expected to be opened as early as 20 15.
I hope I can help you.