Hmm. Just opened agenda.community in-app on macOS to see these. Has Unown taken over, or did I do something wrong?
I’ve never seen this, does it still happen when you quit and relaunch the app?
Just checked—indeed, it persists past both a quit and relaunch and a reboot (and incidental macOS software update). (I see no such characters on macOS or iOS otherwise, including Discourse instances in browsers.)