Just wanted to add the way your issue showed up in the logs
Jan 13, 2019 22:03:33.604 [15052] DEBUG - PublicAddressManager: Obtaining public address and mapping port.
Jan 13, 2019 22:03:33.604 [14192] DEBUG - NAT: UPnP, attempting port mapping.
Jan 13, 2019 22:03:42.645 [14192] DEBUG - NAT: UPnP, didn't find usable IGD.
Jan 13, 2019 22:03:42.645 [14192] DEBUG - NAT: PMP, attempting mapping.
Jan 13, 2019 22:03:42.645 [14192] WARN - NAT: PMP, got an error: NATPMP_ERR_RECVFROM.
Jan 13, 2019 22:03:42.645 [14192] DEBUG - NAT: UPnP, attempting port mapping.
Jan 13, 2019 22:03:42.645 [14192] DEBUG - NAT: UPnP, not an IGD: <http://192.168.1.152:1990/WFADevice.xml>.
Jan 13, 2019 22:03:42.645 [14192] DEBUG - NAT: UPnP, didn't find usable IGD.
Jan 13, 2019 22:03:42.645 [14192] DEBUG - PublicAddressManager: Mapping failed.
Jan 13, 2019 22:03:42.989 [9476] DEBUG - NAT: UPnP, found device <http://192.168.1.152:1990/WFADevice.xml> with private address <192.168.1.74>
Jan 13, 2019 22:03:42.989 [9476] DEBUG - NAT: UPnP, not an IGD: <http://192.168.1.152:1990/WFADevice.xml>.
Jan 13, 2019 22:03:42.989 [9476] DEBUG - NAT: UPnP, getPublicIP didn't find usable IGD.
Jan 13, 2019 22:03:42.989 [9476] WARN - NAT: PMP, got an error: NATPMP_ERR_RECVFROM.
Not sure what 192.168.1.152 was
Plex Media Server does an SSDP multicast search and router would normally response with details of the interface for the IGD (Internet Gateway Device) - may be 192.168.1.152 was responding
