Hi,
Thanks for your query. I think some of your third party extensions may conflicting. Would you please make sure that you are using
tinymce as your default editor
http://prntscr.com/p6mfy4
We found previously that using JCE causes some issue. Or you can disable any other third party extensions or plugins to check which one is doing the conflicting.
Note: Please make sure that you are using latest version of our pagebuilder.
-Best Regards