I'm at a loss. I get the same as you on the command line. But in my test, running this:

 my $fs4 = {'_structure' => {}};
 say (exists $fs4->{_structure}{'/Users/dotfiles/perl5/my_modules'}{BL
+AH}{Crap});
 d $fs4->{_structure}, 3;
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I get this:

$VAR1 = {
  '/Users/dotfiles/perl5/my_modules' => {
    'BLAH' => {}
  }
};
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