Received with thanks, Mario.
I will come back to commune with this if later I need to.
My script is now working, but I note that this module uses POSIX exits.
Whilst I do not yet understand what exactly the difference is, I am aware it behaves differently.

In reply to Re^2: Parallel::ForkManager dies with "Free to wrong pool..." by perlygapes
in thread Parallel::ForkManager dies with "Free to wrong pool..." by perlygapes

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