The spacing between the number and the text is determined by the setup of numbering under the multi-level list numbering. You should be following the steps shown in How to create numbered headings or outline numbering in Ribbon Versions of Word by Shauna Kelly.

Simply adding spaces in the style, won't work, it has to go through the numbering controls.

Like macropod, I suspect a setting to update the styles. Take a look at the setting in a document created from your template.