Thanks for the sample. Looking at it, I conclude that the font formatting of level 3 is damaged.
Running the macro below will fix the numbering in the sample document. When you run it, the macro will actually process all multilevel lists in the current document, and therefore it may be a bit slow, especially on larger documents. (Maybe someone can improve the macro, making it more efficient.)
You can copy and paste the code into a module in the VBA Editor (Alt+F11 or Alt+Fn+F11 on some keyboards). See https://www.gmayor.com/installing_macro.htm .
Sub FixListNumbering()
'Macro created in November 2025 by MVP Stefan Blom
Dim lt As ListTemplate
Dim i As ListLevel
For Each lt In ActiveDocument.ListTemplates
For Each i In lt.ListLevels
i.Font.Reset
Next i
Next lt
End Sub