Could this be possibly due to issue34769 ? There was another report related to this commit : issue36403

➜  cpython git:(41e5ec377b) git checkout 41e5ec377b && make -s -j4 > /dev/null
HEAD is now at 41e5ec377b bpo-34769: Thread safety for _asyncgen_finalizer_hook(). (GH-9716)
➜  cpython git:(41e5ec377b) ./python.exe ../backups/bpo36449.py
aenter
Traceback (most recent call last):
  File "../backups/bpo36449.py", line 25, in <module>
    loop.run_until_complete(main())
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/asyncio/base_events.py", line 573, in run_until_complete
    return future.result()
  File "../backups/bpo36449.py", line 20, in main
    raise Exception
Exception
➜  cpython git:(41e5ec377b) git checkout 41e5ec377b~1 && make -s -j4 > /dev/null
Previous HEAD position was 41e5ec377b bpo-34769: Thread safety for _asyncgen_finalizer_hook(). (GH-9716)
HEAD is now at 0ce31d340b bpo-32962: Fix test_gdb failure in debug build with -mcet -fcf-protection -O0 (GH-9656)
➜  cpython git:(0ce31d340b) ./python.exe ../backups/bpo36449.py
aenter
aexit
Traceback (most recent call last):
  File "../backups/bpo36449.py", line 25, in <module>
    loop.run_until_complete(main())
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/asyncio/base_events.py", line 576, in run_until_complete
    return future.result()
  File "../backups/bpo36449.py", line 20, in main
    raise Exception
Exception