The theme is only supposed to display the excerpt if a manual excerpt has been written for the particular page/post. If the excerpt is empty, there is no excerpt to display so an excerpt should not appear.
From what you have said, it sounds like you have a plugin that is automatically generating excerpts from the full content of all your pages, and then the theme “sees” this as a manually added excerpt and thus displays it.
It would be a big help if you please let me know what plugins are active on your site, so that we can look into this and update the theme to stop this from happening.
Thanks in advance.