The Luci DDNS is third-party services, so if a DDNS service occur didn't update IP problems, it may cause VPN connection exceptions. As GL cannot verify whether its DDNS/domain name service is normal.
In addition, the GL GUI is not currently compatible with third-party DDNS services. If you have added DDNS services in the Luci, can customize modify wg .conf or .ovpn file.