The link to Twitter and GitHub is gone, and I'm pretty sure I added some weeks ago, and I had ir for some time... I will add it again tomorrow and I will keep an eye on it to see if it goes away again or if the potential bug was fixed.
Discussion
Was it there for some time? It could be that another app is deleting them if they don't support these identity fields.
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.