This is a known bug, where the program will not allow transitions on the last line of a page.  If you have several short scenes in a row that use transitions, this can cause them all to be pushed to the next page creating a very short page.  To correct this, please download and install the latest version (4.8.12).

Before installing, it is always a good idea to back up your scripts first.

Download Movie Magic Screenwriter 4.8.12