Some spoiler images and other images are not being served properly. We’re still figuring out what’s going on with the middleware we use to serve this content. As for spoilers not spoiling - fluffy pony grimdark is hidden by default and fluffy pony is spoilered by default. These both work. Heck, all but one image in your post are spoilered; that appears to be an image where the tag is not present where it should be or your settings are overriding it.

The get correctly spoilered for me.  
Don’t know what to think.  
Report it to Clover.

Hovering over the images shows they do have the “fluffy pony” tag.

Did you check if the images were properly tagged in the exact same moment they were listed?  
Maybe someone tagged them later.

There’s a simple reason.
 
You’re not helping derpibooru at all. Donate some money, upload less ‘frivolous’ images to reduce its clutter. Otherwise, its problems will increase the way ponibooru’s did.

TheAbridgenator  
I lol’d

No, it’s tagged properly. Still not spoilered.

And they weren’t tagged properly because they were uploaded by somebody who enjoys fluffy ponies, meaning they don’t have a brain.

Second image, last row. Tagged properly, but not spoilered.

The fluffy pony images that aren’t spoilered weren’t probably tagged properly.

The images are getting spoilered, can’t you see?  
They aren’t hidden.
 
And the broken images because magic.