env_subproc_init = SubprocVectorEnv(
        [lambda: SimpleEnv() for _ in range(8)])
for _ in range(2000):
        c = Collector(policy, env_subproc_ini, buffer)
        c.close()

A broken pipe error will be reported. Seems that SubprocVectorEnv is not actually released and cannot be reused once assigned to a collector. I don't know if this can be counted as a bug.
BrokenPipeError: [Errno 32] Broken pipe