When you cannot access the web interface, can you ping 192.168.1.2? Maybe you can try to modify your IP again and change your username/password.

Maybe you can change the PVID of port1 to 2. The port1 belongs to VLAN2 and it's untagged. Only the PVID of port1 is 2, the data from port1 will belongs to VLAN2.

I should say 'If the link aggregation is failed, when you link 3 cables on the switch, it will causes the broadcast storm.’ If the broadcast storm happens, you will see the lights on the switch blink...

I don't know whether TL-SG108 can work with XS4ALL. But my TL-SG108 is work perfectly now.

I haven't meet this problem. But I think the switch should have the CPU monitor. If you doubt that it's related to the CPU, I think you can check the monitor.

When you add the three ports to the second VLAN, the three ports should be able to remove from VLAN1. But as I know, TL-SL5428 is old version Switch of TP-LINK, I also cannot make sure it.:p