It's not suggested to upgrade and you may get error message failed to ugprade, because you have different country version. Before the new firmware release, you can concerntrate on do some...

it seems very strange, how far is between your main router and the extender, if you put them a little bit closer? Will you still encounter this problem?

You can try to check the link speed, normally for wirelss connection, the real downlaod speed should be 60% of the link a speed, I find a FAQ on TP-Link Website for how to check the link speed...

Hey mate, What's the model number for your switch, is it HS200? Netural should always connect to netural wire.

Currently, there is no such button to turn that light off, I feedback to tplink, they said will report to product engineer.

Have you tired to reset it and redo the configuration, it seems you encountered a quite strange issue