Problems with formatting heading in Word

Hi,

I'm writing a long text in Word. The chapters are formatted with numbered headings. For chapters 1 - 9 everything looked good - but as soon as I jumped to chapter 10, I had this huge space between numbering and chapter text. I have looked everywhere in the formatting - but there is no tab or space or anything. Has anyone an idea where this is coming from and how I can get rid of it?

thanks and best regards

Hagbard