Where does @current_list and @temp_list come from? They seem to be global variables declared elsewhere in your script. To see what they actually contain use Data::Dumper to print them out, and do the same for @current_devicelist and @temp_devicelist. Insert this code and come back with the results - and don't forget to use code tags:

use Data::Dumper;

test_updatedevice();

sub test_updatedevice {
    print Dumper(\@current_list);
    print Dumper(\@temp_list);

    my $Device_LINK = 
        $server->object("ICF_PersistentDataSet",$devicelinks);
    my $Temp_Device_LINK = 
        $server->object("ICF_PersistentDataSet",$tempdevicelinks);
    
    my $current_devicelist = $Device_LINK->invoke("get");
    my $temp_devicelist = $Temp_Device_LINK->invoke("get");
    
    print Dumper($current_devicelist);
    print Dumper($temp_devicelist);
}
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