Can't use WWAN0 after bridge

I am using a Telit LE910C1 modem and a 4G/LTE HAT in ECM mode. Everything works great, I can ping using the cellular interface. I followed this guide to set up a wifi hotspot (wlan0) with the cellular connection (wwan0).

After wlan0 and wwan0 are bridged, I receive Destination Host Unreachable when trying ping -I wwan0
I use a wireguard interface on the device to SSH past AT&T’s CGNAT. It seems like when the bridge is up, the Pi can’t use the wwan0 connection. Is there a way to fix this so that the wireguard interface (wg0) can be bridged to wwan0 as well as wlan0?