Looks like the host is blocking imgbb<dot>com and ibb<dot>co as a 'known DB injection domain', and that's beyond my control. Don't use that image host(s). Your post should display if the post is already here, but when you try to edit it the host's attack block script stops your edit.
Beyond that, I need a specific day and IP address when the error occurs. The raw access logs are WAY too effing big to filter through otherwise.
I've edited the 403 page to put this notice at the bottom... maybe it'll quell a few comments from people that haven't seen this thread.