If you copy/pasted this text from another application there’s a chance these non-breaking spaces were copied over. Retyping the heading text manually should resolve the issue
Some formatting crawled into the text that you have copied from somewhere. Make sure to paste it as non-formatted plain text (one way is to copy your text into the text editor like notepad or the mac alternative and then copy-paste it from there so that all the text formatting is cleared. Another way is to paste the text with ctrl/cmd+shift+v instead of ctrl/cmd+v - this clears the formatting).
Thanks for that. I have tried to follow your instructions but am appearing to have the same problems. I set up a style sheet - that’s the only place I have been copying stuff from.
It looks like it is doing it for all my headings - where I set the headings styles as the defaults.