It still could be a theme issue. I suggest that you copy the page and put the copy out of reach to the public so you can work with it unnoticed. Then on the copy, remove all other modules from the page then try changing the theme to several other themes, and make sure you chage the container several times. When changing the container, also test containers from other themes. Test the visibility of your content in the HTML module in edit mode with each incremental change that you make.