Hi

I'm struggling to get this extender to work.
First, here is my setup.

I have the router on the second floor in my house, the router is connected to a 5G receiver situated on the roof above.
I have a network cable going down to first floor, put into a switch. 
I bought the RE305 and have been trying to connect it to the switch and replicate the same wifi network on the first floor.
The problem is that when I connect the RE305 the complete network goes down, all my smart devices lose connection.

Am I using the wrong unit (RE305) for the thing I want to achieve?