Sorry for the inconvenience.
Do you use multilevel list?
If yes, please check the format of "Link level to style" and the style for that option.
Please back up your document, then I suggest you click Alt+Ctrl+shift+S to open Styles pane.
Right-click the "Heading 2" style, click "Select All xx Instance(s)", then click "No Spacing" in the Task Pane. Check whether this step could change the format back.
If this issue also occurs with other documents.
It's recommended to rename the Normal template (Normal.dotm) for a test.
- Please close all the files of Office and go to File explorer > View in Show/hide group > check the box of "Hidden Items".
- Go to C:\Users\<user name >\AppData\Roaming\Microsoft\Templates, then find the Normal.dotm and rename it. This file will be automatically generated when reopen Word.
Hope this information is helpful.
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