Thanks for sharing your code. Hopefully someone more knowledgable than myself can reply. I was hitting a similar (but not the same) problem where my store.dispatch contained some Core Data related code that was not following proper managed object thread containment rules. (It mostly worked, except for sometimes. 
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A random thought I had. Is it okay for the different async child tasks to use the continuation variable concurrently? IOW, is continuation.yield re-enterant?