Does this phenomenon occur with all files and sites or just certain ones?
Are you working with valid HTML and CSS code?
I contacted Adobe Support and they login to my computer and they could not solve the issue, so the issue was sent to a higher level of support, still waiting!
I don't like giving up and I found the error myself. For some reason in the MacOS Library - preferences when I upgraded to Catalina it was having issues with some of the preference files, so I installed Dreamweaver and then deleted and preferences that were linked to Dreamweaver that were not auto-deleted and this correct the error
I can now see my site and all the CSS files again 😉