@anonymity 这篇是原理： https://openwrt.org/docs/guide-user/network/wan/multiwan/mwan3
1 Restore mark if previous set. If successful marked, goto step 5.
2 Check if the packet arrives on a wan interface. If originated from a local connected ip network, then mark packet with default iface_id. If the packet is from another (non-local) network and arrives on wan interface, then mark it with iface_id. If successful marked, goto step 5.
3 Check if packet destined for a known ip network (has a route for it other than default). If so then mark packet with default iface_id and goto step 5.
4 Check if packet source address is that of a wan interface. If so use that wan interface for routing regardless of user defined rules and mark packet with iface_id of corresponding wan.
5 Apply user rules and mark with configured iface_id. If no match leave unmarked.
6 If marked then save mark.

第 2 步已经包含源进源出了，目标地址是出站分流用的，你折腾 in 填内网 IP 没用。mwan3 底层是 pbr 和 hotplug.d, 用 ip rule 和 ip route show table x 排查一下有没有问题，default 走 wan0 大概是前面几步就没配对，你先看下接口上线了没有优先级对不对。