Paste into HTML email

 I am not able to cut from documents, etc. and paste content into XFinity email when in the HTML mode.  (If I switch to text I can paste, and then I can switch back to HTML to finish composing a message).  

I noticed this was a topic in past forums, about 2017, but the threads are locked, and certainly the software is different.

Does anyone know why this is happening and if there is a solution?