@coco-ant,

My first general thought is that this may be in relation to the fact that the devices can be controlled locally when connected to the same network, or through a service such as your Smart Hubs. If your phone is not connected to the network, do you still see the same results in your log?

Are you able to verify that your main network cannot see the IoT devices and that you cannot ping them from a device on the main network?

More likely, however, is that it could also just be a way in which your modem is processing and logging the data. While the VLAN will separate out your networks locally, all of your data is still eventually ending up having to go through your public IP address. Also, Unless you have a separate DHCP server for your IoT VLAN this also means that your IoT devices are receiving their addresses from the main router also.