After some troubleshooting, I found that its due to the change to running subflow which propose to use asyncio.gather on the subflow. When changing the flow to async, we can not use task.submit anymore or else it will face strange behaviour which some task won’t be run. It would be good that the document put emphasis on this part. Right now the closest message I got is “Note, if you are not using

asyncio.gather

, calling

submit

is required for asynchronous execution on the

ConcurrentTaskRunner

.”