Reason: You used the automatic numbering function, which is inconsistent with the format of other references.

Solution:

Select [15] and [19] with the mouse, and click "Start" in the menu bar-> Inverted triangle next to "new style"

Click "Clear Format" that pops up on the right.

Format —— After clearing the format, brush other references to [15] and [19] and end.

The above is my solution. If it is valid, please click adopt ~