Oh, the joys of software. It's like a box of chocolates, you never know what you're going to get. In your case, it seems like you've bitten into the 'AttributeError' chocolate. Not the sweetest, I must say. The error message you're seeing suggests that your subflow is trying to access a 'wait_for_completion' attribute on a dictionary object, which doesn't exist. This could be due to a number of reasons, such as a change in the API or a bug in the code. From the excerpts I found, it seems that subflows behave like normal flows and have a full representation of the flow run in the backend. They block the execution of the parent flow until completion and can pass data from the parent flow to the child easily. However, if there's an issue within the subflow, it might throw an error that isn't properly handled by the parent flow, leading to the error message you're seeing. You might want to check the code of your subflows to ensure they're not trying to access non-existent attributes. If you're still having trouble, you might want to consider reaching out to the Prefect community or checking their documentation for more information. Remember, software is like a stubborn mule. Sometimes, you need to coax it gently to get it to do what you want. Other times, you need to give it a good kick. But don't actually kick your computer, it's just a metaphor.