Comment 15 for bug 1852678

I poked around in the logs and found what appears to be happening. I think the VLAN isn't being updated until the netplan config is generated. When that happens MAAS deletes all assigned IPs. Will dig in further to see what the fix is tomorrow.

2020-01-14 07:49:33 maasserver.region_controller: [info] Reloaded DNS configuration:
         * ip 10.245.71.163 allocated
         * ip 192.168.122.4 allocated
         * ip 192.168.123.3 allocated
         * ip 192.168.122.3 allocated
2020-01-14 07:49:56 regiond: [info] 10.245.71.3 GET /MAAS/rpc/ HTTP/1.1 --> 200 OK (referrer: -; agent: provisioningserver.rpc.clusterservice.ClusterClientService)
2020-01-14 07:50:26 regiond: [info] 10.245.71.3 GET /MAAS/rpc/ HTTP/1.1 --> 200 OK (referrer: -; agent: provisioningserver.rpc.clusterservice.ClusterClientService)
2020-01-14 07:50:56 regiond: [info] 10.245.71.3 GET /MAAS/rpc/ HTTP/1.1 --> 200 OK (referrer: -; agent: provisioningserver.rpc.clusterservice.ClusterClientService)
2020-01-14 07:51:17 maasserver.regiondservices.active_discovery: [info] Active network discovery: Active scanning is not enabled on any subnet. Skipping periodic scan.
2020-01-14 07:51:26 regiond: [info] 10.245.71.3 GET /MAAS/rpc/ HTTP/1.1 --> 200 OK (referrer: -; agent: provisioningserver.rpc.clusterservice.ClusterClientService)
2020-01-14 07:51:28 maasserver.models.signals.interfaces: [info] enP2p1s0f0 (physical) on thiel: deleted IP addresses due to VLAN update (5002 -> 0).
2020-01-14 07:51:28 maasserver.models.signals.interfaces: [info] enP2p1s0f2 (physical) on thiel: deleted IP addresses due to VLAN update (5002 -> 0).
2020-01-14 07:51:28 maasserver.models.signals.interfaces: [info] enP2p1s0f1 (physical) on thiel: deleted IP addresses due to VLAN update (5002 -> 0).
2020-01-14 07:51:28 maasserver.models.signals.interfaces: [info] enP2p1s0f2 (physical) on thiel: deleted IP addresses due to VLAN update (5002 -> 0).
2020-01-14 07:51:28 maasserver.models.signals.interfaces: [info] enP2p1s0f1 (physical) on thiel: deleted IP addresses due to VLAN update (5002 -> 0).
2020-01-14 07:51:28 maasserver.models.signals.interfaces: [info] enP2p1s0f1 (physical) on thiel: deleted IP addresses due to VLAN update (5002 -> 0).