Was it there for some time? It could be that another app is deleting them if they don't support these identity fields.
Discussion
I am not sure about it. I added tem back again (in amethyst; the other references were there all the time). You can check them in my amethyst profile now
These identity tags use an i tag together with follows and the relay list. Which means if apps are not preserving i tags, they could simply erase it when you follow/unfollow or change relays.
It's similar to the private bookmarks that get deleted in Snort when you change the public ones.