I've been using imagebuilder to bake openwrt 19.07 images for couple of years on multiple devices and everything worked out fine.
I'm now testing baking same same config for 21.07, I just applied minor diffs following this https://openwrt.org/releases/21.02/notes-21.02.0 and comparing the /etc/config/network file autoconverted by luci.
I was experiencing wireguard working only for a fraction of a second at boot and watchcat rebooting even if Internet connection was apparently working, then I realized that stopping mwan3 solved the problem.
mwan3 was showing correct status and was responsive in handling new wan connections, but some applications were unable to route packets correctly. It is clearly a mwan3 routing table problem as
ip r get <wg sub address> reports wrong gateway.
I'm reverting to 19.07 for now, any ideas?