FYI, I updated the patch I linked in Pastebin. Instead of having to switch over to my Bridger fork, you can stick with Felix's source and run the following in your OpenWrt build system to apply the updated patch to turn on debug output:
mkdir package/network/services/bridger/patches && curl -o package/network/services/bridger/patches/001-enable-debug-output.patch https://pastebin.com/raw/5TY3hema
Otherwise, refer to my prior post for ways you can output the debug info once you build from this patch.