You have a typo on declaring $cv_ref, you spell summary wrong.

this works for me:

my $vm_view = Vim::find_entity_views(
    view_type  => 'VirtualMachine',
    filter    => { 'guest.guestState' => 'running' },
    properties => [ 'summary.customValue', 'name', ],
);

for my $vm ( sort { $a->name cmp $b->name } @$vm_view ) {
    my $cv_ref = $vm->{'summary.customValue'};
    next unless defined ( $vm->{'summary.customValue'} ) ;
    print $vm->name . "\n";
    for ( @$cv_ref ) {
        #next unless defined $_->value;
        print "key: ", $_->key, "\tvalue: ", $_->value, "\n";
    }
}

$perl /tmp/kk

vmname

key: 201    value: bladibla

key: 203    value: globalbladibla