Found a Now Support article that may resolve this for you: https://support.servicenow.com/kb?id=kb_article_view&sysparm_article=KB2065941

The basics of it are: 

1. Set the system property "glide.ui.html.editor.paste.html_import" to "merge". 
2. Set the system property "glide.ui.html.editor.v4.paste.html_import" to "merge".

This addressed the issue for me.