mpi_algo_factory fails with double-digit cores on MacOS

[20DM]

The mpi_algo_factory unit test runs fine for up to 9 cores on my Mac but starting with 10 it seg-faults immediately:

mpi_algo_factory.cc:71: FAILED:
  {Unknown expression after the reported line}
due to a fatal error condition:
  SIGTERM - Termination request signal
...
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prterun noticed that process rank 9 with PID 21680 on node eduroam-int-dhcp-97-149-91 exited on
signal 11 (Segmentation fault: 11).
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