CPython does most of its memory management by reference counting, which fails to reclaim circular structure. So to make sure it gets everything, it occasionally runs a conventional tracing GC. If the GC happens to run just after you create that async task, the task itself can get collected, it sounds like. It's good to know about this and is (my own editorializing) yet another reason Python3 should have used Erlang-style concurrency instead of this async stuff.