Apply attached manager_timeout.patch and run the command:

    ./python -m test --fail-env-changed test_multiprocessing_spawn -v -m test_rapid_restart -F -j4

If you fail to reproduce the issue, replace -j4 with -j10 or use a larger number of concurrent jobs.

Output:
---
(...)
0:00:00 load avg: 2.85 Run tests in parallel using 4 child processes
0:00:06 load avg: 3.02 [  1/1] test_multiprocessing_spawn failed (env changed)
test_rapid_restart (test.test_multiprocessing_spawn.WithManagerTestManagerRestart) ... ok

test_rapid_restart (test.test_multiprocessing_spawn.WithProcessesTestManagerRestart) ... ok
Warning -- Dangling processes: {<SpawnProcess name='QueueManager-5' pid=438355 parent=438255 stopped exitcode=-SIGTERM>, <SpawnProcess name='QueueManager-7' pid=438395 parent=438255 stopped exitcode=-SIGTERM>}

test_rapid_restart (test.test_multiprocessing_spawn.WithThreadsTestManagerRestart) ... ok
Warning -- Dangling processes: {<SpawnProcess name='QueueManager-8' pid=438423 parent=438255 stopped exitcode=-SIGTERM>, <SpawnProcess name='QueueManager-9' pid=438456 parent=438255 stopped exitcode=-SIGTERM>}
Warning -- Dangling processes: {<SpawnProcess name='QueueManager-8' pid=438423 parent=438255 stopped exitcode=-SIGTERM>, <SpawnProcess name='QueueManager-9' pid=438456 parent=438255 stopped exitcode=-SIGTERM>}

----------------------------------------------------------------------
Ran 3 tests in 5.404s

OK
Kill <TestWorkerProcess #2 running test=test_multiprocessing_spawn pid=438256 time=6.9 sec> process group
Kill <TestWorkerProcess #3 running test=test_multiprocessing_spawn pid=438259 time=6.9 sec> process group
Kill <TestWorkerProcess #4 running test=test_multiprocessing_spawn pid=438260 time=6.9 sec> process group

== Tests result: ENV CHANGED ==

1 test altered the execution environment:
    test_multiprocessing_spawn

(...)
---


Examples of similar old issues:

* bpo-39932 at https://bugs.python.org/issue39932#msg363925 : <ForkServerProcess(QueueManager-2036, stopped[1])>
* bpo-38447: <SpawnProcess(QueueManager-1576, stopped)>
* bpo-38796: <SpawnProcess name='QueueManager-327' pid=60315 parent=59088 started>
* bpo-34150: <SpawnProcess(QueueManager-181, stopped)>
* bpo-31069 at https://bugs.python.org/issue31069#msg301339 : <ForkServerProcess(QueueManager-465, stopped)>

See also the old fixed bpo-31234 "Make support.threading_cleanup() stricter".