Not the parent, but I've seen it and it's hard to say, 5.5 was being stupidly proactive in monitoring a long-running process in a sub-agent to the point of chowing tokens by continually monitoring.

I queried it and was told that sub-agents can't run processes a blocking fashion, I'm not sure the harness changed, or the model was handling it differently, but it require some changes to skills to prompt around it.