DNS Failing with Mult-Wan Failover Configuration

[obnauticus]

Hello,

I followed this (https://docs.opnsense.org/manual/how-tos/multiwan.html) guide to configure my USB-tethered phone as a backup route in case my primary WAN ethernet interface goes down.

The phone rebooted for an update overnight, it came back up but expectedly didn't have its tethering interface enabled. The WAN interface was up the entire time; however, when the USB ethernet interface went down, DNS requests started failing on the LAN side (despite me having internet access). In System->Settings->General I do have DNS servers configured for both WAN interfaces.

Is there anything special that I need to do to account for this? Do I need to enable "Gateway switching" in System->Settings->General (the guide does not say to do this)? I would like to be able to reboot the phone to perform updates routinely and I realize that I should get a dedicated cell modem to do this, eventually I will but using a spare phone seems like a suitable solution for a hasty backup. Any help is appreciated here.

I followed the part of the guide where you setup a LAN rule to pass DNS traffic (screenshot link below).

https://imgur.com/a/ZyDSeCa