Sandbox: https://codesandbox.io/s/cranky-kapitsa-op3jh

Repro: type "a" and then after a second "b"

Expected: Eventually you'll see "ab" in all fields. Pending "..." indicator goes away.

Actual: You'll keep seeing "a" in low pri field. Pending "..." indicator is stuck.
runWithPriority(
    priorityLevel < UserBlockingPriority ? UserBlockingPriority : priorityLevel,
    () => {
      setPending(true);
    },
  );
  runWithPriority(
    priorityLevel > NormalPriority ? NormalPriority : priorityLevel,
    () => {
      const previousConfig = ReactCurrentBatchConfig.suspense;
      ReactCurrentBatchConfig.suspense = config === undefined ? null : config;
      try {
        setPending(false);
        callback();
      } finally {
        ReactCurrentBatchConfig.suspense = previousConfig;
      }
    },
  );
}
function mountTransition(
  config: SuspenseConfig | void | null,
): [(() => void) => void, boolean] {
  const [isPending, setPending] = mountState(false);
  const start = mountCallback(startTransition.bind(null, setPending, config), [
    setPending,
    config,
  ]);
  return [start, isPending];
}