airport extreme can't connect more than ten devices to internet

Hi, I am trying to connect 20 laptops to our Airport Express, but whenever I approach ten devices connected to the device, it crashes and starts flashing yellow. Does anyone know what the problem could be?

My settings:

Connectr using DHCP

IPv4 Address 10.179.4.244

Subnet Mask: 255.255.240.0

Router Address 10.179.1.1

DNS Servers:

156.1.180.202

156.1.180.201

Configure IPv6 automatically

IPv6 mode: tunnel

Router Mode: Off (Bridge Mode)