I am running Matlab R2020b on a macOS Catalina. I have had this problem a couple of times now with my Livescripts. I will be working on a Livescript and at some point I can no longer add anything except text. As you see in the image below, all the options are greyed out. Closing and opening the document doesn't fix it, nor does resarting Matlab or doing a save as, which make me think is is some underlying file problem. I end up coping the contents over to a new livesript and save it as a new file. When I do that, everything is just fine.