The most common trigger is having one or more long paragraphs of dialogue (usually over a page in length) somewhere in the document. This mostly happens in stage plays where there can be monologues that go on for a while. Please break up those paragraphs with something like Action and see if the program runs better. You can also try and set the program to break Action and Dialogue *only* at sentences ends under Format > Element Styles > Page Breaks.
Another trigger is having blank elements in the document. Click on Tools > Run SmartCheck and click OK to have the program remove any blank elements it finds.
You can also copy and paste your entire document into a new blank document of the same type, i.e., Screenplay, Novel, Stage Play, etc. which may help correct the problem.