It's so awful, and I don't know why. This is the only place I've ever had issues editing posts and it's frustratingly bad.
It won't let you change headers, add spoiler blocks, add images, delete images, add tables, and etc.
It's not consistent either. SOMETIMES it lets you, and other times it's like the system just has a tantrum, folds its arms and just decides that a post is the way it is and there's nothing you can do to change things.
Thanks for reading,