A client had this very strange issue, they thought it was a resources issue since their Hostinger account was telling them that they were nearly out of resources.

After spending an hour checking all the major things I looked at the draft post in question and saw that it was full of... emojis. Now why wouldn't Wordpress want you to insert emojis into a post? Their native editor is called Gutenberg, the inventor of the printing press, surely they don't have such a bizarre requirement.

Nope, it's the emojis. Remove the emojis and it will publish.