There are two common causes of template conflicts.
If individual users have different definitions for the various List Templates involved, the numbering breaks each time a different user opens the document. I recommend that you orphan Normal style so that it is not used in the document, and ensure that none of the styles that contain numbering in the document are based upon it. This lessens the number of times you will suffer the problem.
The second conflict occurs if any document with numbering is attached to its template with "Automatically update styles on open" set to ON. Each time you open the document, Word resets the style. This either conflicts with or resets the List Template, and breaks the numbering.