You have a different list of default relays in Iris and Damus. If you posted a note on Damus, it might not show up on Iris unless you change your relay list.

Tip: add wss://nostr.mutinywallet.com to all of your relay lists. It's a write-only relay that will forward your events out to every known relay that will accept them, over 100. If you publish notes that way you'll always see them in every client and so will your followers.