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user_id=81797

This is definitely not a Python problem.  If I run your
script from two terminal windows from Python directly, they
both finish at the same time.  So, this is either something
in how your browser or proxy is sending requests (perhaps
there is some serialization going on in there), or something
with how your web server is handling the requests.  I can't
say for sure, but it's unlikely to be an issue with Python.
 I'm closing this ticket because of that.