What I described in text is exactly the same bug.
But what I showed in the screenshots is something new that’s appeared in Nightly in the last 2-3 days. Subagent statuses in Agent chat are broken, and the Subagent chat doesn’t open until they complete the task, making monitoring Subagents impossible.
Or maybe this bug just showed up for me today and decided to stick around. 
Subagents’s end-of-work time is also broken, and it starts counting from the moment the chat with them is opened.