No idea about your main problem, but there is a bug in your call of the sub. It should be:

my $pid = db_forkin($dbh, \@some_array_of_files);
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If you had warnings on, you would have gotten a notice about it so I guess you don't. Big mistake

AFAIK there is no fork on Windows so it is simulated with threads. Maybe you could test your script on linux to see whether that changes anything