Sorry about this.
We did test that comments were migrating properly, but it seems some may have slipped through the net.
Unless we discover that this is a really widespread problem, it’s probably going to be quite hard to fix retrospectively now, as we’d have to merge the old and new comments.
It was noticeable that in the previous system relatively few images attracted comments, and our hope is that by making comments more prominent in the new system, images will start attracting a bit more discussion.