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Hello,
already faced a little similar issue coming from formatted text in products description that broke the listing theme.

If that can helps, and as said Jetx :
- try to remove all html formated tags (no <strong>, no link <a href="">, no italic <i>, etc..) by cliking on the "<>" (code source) while editing the description on products page.
- Don't copy/paste texts (from another text editor for example) in description or verify it doesn't copy formatted html tags.
- For the SEO part, maybe try to "save and go back to catalog" a first time, then try again to fill fields.
- for videos : make sure you enabled in Shop Parameters > General > "Allow iframes on HTML fields"