https://forum.netgate.com/topic/138672

config.xml-interfaces

                <opt1>
                        <descr><![CDATA[WAN_<removed>]]></descr>
                        <if>em0</if>
                        <spoofmac></spoofmac>
                        <enable></enable>
                        <alias-address></alias-address>
                        <alias-subnet>32</alias-subnet>
                        <blockpriv></blockpriv>
                        <blockbogons></blockbogons>
                        <ipaddr>xxx.xxx.xxx.250</ipaddr>
                        <subnet>29</subnet>
                        <gateway>WANGW_SC</gateway>
                </opt1>
        </interfaces>
                
        <virtualip>
                <vip>
                        <mode>ipalias</mode>
                        <interface>opt1</interface>
                        <descr><![CDATA[<removed>]]></descr>
                        <type>single</type>
                        <subnet_bits>29</subnet_bits>
                        <subnet>xxx.xxx.xxx.251</subnet>
                        <uniqid>5c0ff05ea3646</uniqid>
                </vip>
                <vip>
                        <mode>ipalias</mode>
                        <interface>opt1</interface>
                        <descr><![CDATA[Unused public IPv4 address]]></descr>
                        <type>single</type>
                        <subnet_bits>29</subnet_bits>
                        <subnet>xxx.xxx.xxx.252</subnet>
                        <uniqid>5c0ff05ea367b</uniqid>
                </vip>
                <vip>
                        <mode>ipalias</mode>
                        <interface>opt1</interface>
                        <descr><![CDATA[Unused public IPv4 address]]></descr>
                        <type>single</type>
                        <subnet_bits>29</subnet_bits>
                        <subnet>xxx.xxx.xxx.xxx.253</subnet>
                        <uniqid>5c0ff05ea36a1</uniqid>
                </vip>
                <vip>
                        <mode>ipalias</mode>
                        <interface>opt1</interface>
                        <descr><![CDATA[Unused public IPv4 address]]></descr>
                        <type>single</type>
                        <subnet_bits>29</subnet_bits>
                        <subnet>xxx.xxx.xxx.xxx.254</subnet>
                        <uniqid>5c0ff05ea36c2</uniqid>
                </vip>
        </virtualip>

config.xml-OpenVPN-bad

                <openvpn-server>
                        <vpnid>1</vpnid>
                        <mode>p2p_tls</mode>
                        <protocol>UDP4</protocol>
                        <dev_mode>tun</dev_mode>
                        <interface>opt1</interface>
                        <ipaddr></ipaddr>
                        <local_port>1194</local_port>
                        <description><![CDATA[Test instance]]></description>
[...]
                </openvpn-server>

config.xml-OpenVPN-good

                        <vpnid>1</vpnid>
                        <mode>p2p_tls</mode>
                        <protocol>UDP4</protocol>
                        <dev_mode>tun</dev_mode>
                        <interface>_vip5c0ff05ea3646</interface>
                        <ipaddr>xxx.xxx.xxx.251</ipaddr>
                        <local_port>1194</local_port>
                        <description><![CDATA[Test instance]]></description>
[...]
                </openvpn-server>

ifconfig

# ifconfig
em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
	options=1209b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,WOL_MAGIC,VLAN_HWFILTER>
	ether 00:25:xx:xx:xx
	hwaddr 00:25:90:95:19:94
	inet6 <removed>%em0 prefixlen 64 scopeid 0x1 
	inet xxx.xxx.xxx.xxx.250 netmask 0xfffffff8 broadcast 81.63.144.255 
	inet xxx.xxx.xxx.xxx.251 netmask 0xfffffff8 broadcast 81.63.144.255 
	inet xxx.xxx.xxx.xxx.252 netmask 0xfffffff8 broadcast 81.63.144.255 
	inet xxx.xxx.xxx.xxx.253 netmask 0xfffffff8 broadcast 81.63.144.255 
	inet xxx.xxx.xxx.xxx.254 netmask 0xfffffff8 broadcast 81.63.144.255 
	nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
	media: Ethernet autoselect (1000baseT <full-duplex>)
	status: active
em1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
	options=209b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,WOL_MAGIC>
	ether 00:25:xx:xx:xx
	hwaddr 00:25:90:95:19:95
	inet6 <removed>%em1 prefixlen 64 scopeid 0x2 
	inet 192.168.1.1 netmask 0xffffff00 broadcast 192.168.1.255 
	nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
	media: Ethernet autoselect (1000baseT <full-duplex>)
	status: active
[...]
ovpns1: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> metric 0 mtu 1500
	options=80000<LINKSTATE>
	inet6 <removed>%ovpns1 prefixlen 64 scopeid 0x9 
	inet 192.168.100.1 --> 192.168.100.2 netmask 0xffffff00 
	nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
	groups: tun openvpn 
	Opened by PID 983

server1.conf-bad

dev ovpns1
[...]
local xxx.xxx.xxx.251

server1.conf-good

dev ovpns1
[...]
local xxx.xxx.xxx.251

sockstat-bad

# sockstat -l -4 | grep 1194
root     openvpn    983   6  udp4   xxx.xxx.xxx.251:1194    *:*

sockstat-good

# sockstat -l -4 | grep 1194
root     openvpn    92014 6  udp4   xxx.xxx.xxx.xxx:1194    *:*