Cannot set properties of undefined (setting 'parent') about missionary HOT 2 OPEN

(ns main.scratch
  (:require [missionary.core :as ms]))
(comment
  (do
    (def input! (atom true))
    (def task
      (ms/reduce
       (constantly nil)
       (ms/ap
        (let [visible? (ms/?< (ms/watch input!) )]
          (println visible?)
          (if visible?
            (try
              (ms/?> (ms/ap
                      (let [n (ms/?> (ms/seed (range 100)))]
                        (ms/? (ms/sleep 1000))
                        (println "TICK: " n))))
              (catch missionary.Cancelled e
                (ms/amb>)))
            nil)))))
    (when (resolve 'cancel) (cancel))
    (def cancel (task println #(js/console.error %))))

  ;; wait a moment, then run
  (reset! input! false)

;; VM1246:400 TypeError: Cannot set properties of undefined (setting 'parent')
;;     at Object.missionary$impl$Ambiguous$ready [as ready] (Ambiguous.cljs:299:43)
;;     at Function.G__17106__0 [as cljs$core$IFn$_invoke$arity$0] (Ambiguous.cljs:330:28)
;;     at missionary$impl$Ambiguous$transfer (Ambiguous.cljs:251:8)
;;     at Object.eval [as cljs$core$IDeref$_deref$arity$1] (Ambiguous.cljs:11:19)
;;     at Object.cljs$core$_deref [as _deref] (core.cljs:688:12)
;;     at Object.cljs$core$deref [as deref] (core.cljs:1477:4)
;;     at Object.missionary$impl$Ambiguous$backtrack [as backtrack] (Ambiguous.cljs:33:8)
;;     at Object.missionary$impl$Ambiguous$branch [as branch] (Ambiguous.cljs:73:8)
;;     at Object.missionary$impl$Ambiguous$ready [as ready] (Ambiguous.cljs:307:44)
;;     at Function.G__17103__0 [as cljs$core$IFn$_invoke$arity$0] (Ambiguous.cljs:323:28)

  )