I think there is a closing brace missing at the very end of your code. Reason: At the beginning of this while the filehandle $lscore_fh is defined and set.

while (my $currentlist_row = $currentlist_csv->getline_hr($currentlist
+_fh)) {
    
    my $lscore_fh;
    if (exists($lscore{$currentlist_row->{FacID}})) {
        $lscore_fh = $fh{$currentlist_row->{FacID}} //= do {
            open my $f, '>:utf8', $lscore{$currentlist_row->{FacID}};
            $f;
        };
    }
    else {    
        $lscore_fh = $fh{__LSCORE__} //= do {
            open my $f, '>:utf8', $lscore_fallback_file;
            $f;
        };
    }
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The filhandle is still used at the very end of your code, so it has to be within the while loop. So the loop only closes at the very end.