Unable to get R7800 to function in bridge mode

My main router is an R7800 that works flawlessly. I recently bought a second R7800, intending to use it in bridge mode, since I have some wired clients elsewhere in the house. I followed these instructions from the manual:

• Login to new router and go to ADVANCED > Advanced Setup > Wireless Bridge
• Select the "Enable Bridge Mode" check box
• Click the "Setup Bridge Mode Wireless Settings" button and enter the settings of the other router
• I select the 5 GHz option from the drop-down, enter the SSID of my main router, select "WPA2-PSK [AES]" and enter the wi-fi password of that router
• I uncheck "Get IP Address Dynamically" and enter a static IP address & subnet mask for the new router, and then the main router IP address as the gateway
• I click "Apply"

After that, the router reboots. But when it comes back up...no bridge mode. That is, the GUI acts as if it's in bridge mode (various menu items are now disabled, as expected) but it doesn't show up in my wi-fi site survey app and when I connect a client to it via Ethernet, that client has no access to anything. It can't even ping the main router's IP.

It's as if putting it bridge mode somehow disabled its wi-fi radios entirely.

Am I doing something wrong?