@MR.S Yes, I know. The ordered SG3210X-M2 will arrive tomorrow. But this will not resolve the issue because what I described im my previous post happened without the TL-SG108E connected. When I did...

@MR.S If I change the port 10 of the switch to "IoT" and reconnect the device, it gets the correct fixed IP of the "IoT" VLAN. As soon as I change it back to "All", the device cannot be reached any...

@MR.S Yes, this is exactly what I don't understand.

I updated my last reply just as you answered. So this should work, right?

@MR.S No, the Switch is connected via port 2 to LAN4 of the router. Port 2 is the router and port 10 is the one the devices are connected to. Between port 2 and the devices is an old TL-SG108E switch...

@MR.S Yes, for the IoT VLAN all ports of the router are enabled.