Just a thought. I have a Mac but I am no expert. Are you using a template you have used before without getting this issue? If not, check the page layout you are using now to make sure it does not impose a large space at the bottom of the page which inadvertently allows only one paragraph.
If you have a similar document you have created previously, you might try loading it, re-naming it, saving the re-named document and clearing it before using the empty template again for your current document. If that works, save this layout as a named template to use in future.
I hope this helps but as I say, I am not an expert, just another occasional Mac sufferer.