Content Not Published

Sometimes I get a Content Not Published error so I can't publish my post, and I can't tell why.

Content Not Published
Your post contains invalid HTML. Remove the following invalid tags before publishing: a, a (data-bi-type), div, li-image, li-table, li-tcols, li-td, li-tsection

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Most recently, it appeared when I tried to edit spoiler titles where I had two images inside two spoilers (same as you see here), after I had already published the post. I was trying to edit the post. But it would not take it the second time around. I think it has something to do with elements used by the rich text editor. I made the changes by deleting both spoilers and both images, saving the post, refreshing, editing again, adding the spoilers and images back in and saving again. It's very annoying and frustrating like that. It's not a validation error, like when you add a link and it complains about it. It says the post contains invalid HTML.