Sometimes, a problem with a specific gadget or post, when displayed, can affect the appearance of the entire blog. We've known for years, about the mysterious dropped sidebar . Sometimes, we see similar problems, in other blog performance. Gadgets missing. Gadgets visible, but they don't work. Gadgets visible in the desktop view - but not the mobile view (or, vice versa). Posts that are unreadable - or worse, previously published posts, in that index page, that are unreadable. Both the HTML / JavaScript gadget, and the page or post, can be edited either as code ("HTML"), and as displayed ("Compose" / "Rich Text"). If you spend a lot of time in "Compose" / "Rich Text" mode, when editing gadgets, pages and posts, you may not know about "HTML" mode - or its dangers.
What Blogger won't tell you