looking closer, the image type may be a factor. Trying to insert a PDF file from the multiple uploads button also shows a broken image icon in the discussion itself.  When I try to do the same thing on Una.io, it will not let me try to upload a PDF file into the discussion itself, so I think therein lies the problem. I need to find a setting that restricts the filetype that people can upload. It's all a jolly big learning curve for us "non-dev" types :)