Can't connect to devices when connected to mesh node

Btb331

I have a Zyxel EX3301-T0 as the main router and a Wx-3100 as a mesh network extender.

I want to have separate networks for 2.4G and 5g as my phone keeps defaulting to 2.4g when they are on the same ssid.

I have a raspberry Pi which is connected via WiFi to the network. Due to its position, it's connected to the main hub. I can ssh into it via my phone when my phone is connected to the main hub.

However, when I'm closer to the mesh node, my phone connects to the mesh node and then I lose access to the raspberry pi. It's like the mesh nods isn't allowing me to access devices on the main hub.

Please help.