Maybe it's related to bpo-33608:
https://bugs.python.org/issue33608#msg340143


https://buildbot.python.org/all/#/builders/58/builds/2558

0:42:36 load avg: 5.63 [299/423/1] test_venv crashed (Exit code 1)
Timeout (0:35:00)!
Thread 0x00000e00 (most recent call first):
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\subprocess.py", line 1332 in _readerthread
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\threading.py", line 865 in run
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\threading.py", line 923 in _bootstrap_inner
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\threading.py", line 885 in _bootstrap

Thread 0x00000150 (most recent call first):
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\subprocess.py", line 1332 in _readerthread
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\threading.py", line 865 in run
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\threading.py", line 923 in _bootstrap_inner
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\threading.py", line 885 in _bootstrap

Thread 0x00000d40 (most recent call first):
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\threading.py", line 1015 in _wait_for_tstate_lock
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\threading.py", line 999 in join
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\subprocess.py", line 1361 in _communicate
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\subprocess.py", line 999 in communicate
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\test_venv.py", line 40 in check_output
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\test_venv.py", line 327 in test_multiprocessing
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\unittest\case.py", line 628 in _callTestMethod
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\unittest\case.py", line 671 in run
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\unittest\case.py", line 731 in __call__
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\unittest\suite.py", line 122 in run
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\unittest\suite.py", line 84 in __call__
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\unittest\suite.py", line 122 in run
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\unittest\suite.py", line 84 in __call__
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\unittest\suite.py", line 122 in run
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\unittest\suite.py", line 84 in __call__
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\unittest\runner.py", line 176 in run
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\support\__init__.py", line 1984 in _run_suite
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\support\__init__.py", line 2080 in run_unittest
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\libregrtest\runtest.py", line 203 in _test_module
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\libregrtest\runtest.py", line 228 in _runtest_inner2
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\libregrtest\runtest.py", line 264 in _runtest_inner
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\libregrtest\runtest.py", line 135 in _runtest
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\libregrtest\runtest.py", line 187 in runtest
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\libregrtest\runtest_mp.py", line 66 in run_tests_worker
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\libregrtest\main.py", line 611 in _main
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\libregrtest\main.py", line 588 in main
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\libregrtest\main.py", line 663 in main
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\regrtest.py", line 46 in _main
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\regrtest.py", line 50 in <module>
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\runpy.py", line 85 in _run_code
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\runpy.py", line 192 in _run_module_as_main

...

ERROR: test_multiprocessing (test.test_venv.BasicTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\test_venv.py", line 327, in test_multiprocessing
    out, err = check_output([envpy, '-c',
  File "D:\cygwin\home\db3l\buildarea\3.x.bolen-windows7\build\lib\test\test_venv.py", line 42, in check_output
    raise subprocess.CalledProcessError(
subprocess.CalledProcessError: Command '['d:\\temp\\tmpf38yk5w1\\Scripts\\python_d.exe', '-c', 'from multiprocessing import Pool; print(Pool(1).apply_async("Python".lower).get(3))']' returned non-zero exit status 3221225477.


where 3221225477 = 0xc0000005 = EXCEPTION_ACCESS_VIOLATION