pfSense

$i = 0;
foreach($config['ipsec']['phase1'] as $phase1) {
if($phase1['interface'] == "vip131")
$config['ipsec']['phase1'][$i]['interface'] = "wan_vip131";

$i++;
}

This is the upgrade code existing there.
Normally the section with s///g should have taken care of that.
Probably you missed the config version upgrade so missed this?

function upgrade_081_to_082() {
        global $config, $g;
        /* enable the allow IPv6 toggle */
        $config['system']['ipv6allow'] = true;

        /* XXX: Gross hacks in sight */
        write_config();
        if (is_array($config['virtualips']['vip'])) {
                $vipchg = array();
                foreach ($config['virtualips']['vip'] as $vip) {
                        $realif = get_real_interface($vip['interface']);
                        file_put_contents("{$g['tmp_path']}/vipreplace", "s/vip{$vip['vhid']}/{$realif}_vip{$vip['vhid']}/g\n");
                }
                mwexec("/bin/sh -I \"\" -f {$g['tmp_path']}/vipreplace /conf/config.xml");
                require_once("config.lib.inc");
                $config = parse_config(true);
        }
}