Fun indeed! One way to fix this would be to disable lightboxes and pausing animated images inside the spoiler element. It’s very easy to do this with just CSS:
.spoiled {
img.animated,
.lightbox {
pointer-events: none;
}
}
We could also have lightboxing and pausing animations apply only when the contents is unblurred, but that can’t work with the spoiler being a toggle. But if we decide to switch the spoiler behaviour to be one way (unblur on click and that’s it), this could work too.