If this is a bug and it is fixed later on, what is the migration strategy at this point? 🙂

Hey! That sounds weird. I guess it sounds like you wrote something into XT with an edn tag that you're subsequently no longer using / have removed from the environment, and XT can't decode it without a valid reader

Is there a full stacktrace for that?

no hint of what the offending key was?

Basically

(defn get-facts [user-id]
  (xt/q (xt/db node)
        '{:find [(pull u [* {(:user/_id {:as :user/knows}) [:user/rating {:core/skill [:core/name]}]}])]
          :where [[u :xt/id user-id]
                  [u :user/name name]]
          :in [user-id]}
        user-id))

(get-facts #uuid "xxxx")

Hmm, and what happens if you call entity? Does the document look like it only contains regular edn forms? No custom reader tags?