Wireguard metric problem Openwrt(19.07.5 Stable) + Mwan3

[Евгений Глущенко]

There was a problem using wireguard on OpenWrt(19.07.5 Stable) with 
mwan3 package and dynamic routing. The system is configured according to 
the fail over principle.
There are two interfaces (wan and wanb(LTE)) wan interface is the main 
one and everything works fine with it.
But when wan is disabled, all traffic is redirected to wanb, but the 
wireguard continues to use the wan interface, since it has a wan 
interface metric 10 and a wanb metric 20.
All internet user traffic is going out from wan or wanb interface.
On wan
WGClient(10.66.66.3)--VPS(212.x.x.x 10.66.66.1)-wan (172.17.165.64)- 
Openwrt(10.66.66.2 192.168.0.1)-LAN(192.168.0.0/24)
or when wan is down
WGClient(10.66.66.3)--VPS(212.x.x.x 10.66.66.1)-wanb (192.168.8.1)- 
Openwrt(10.66.66.2 192.168.0.1)-LAN(192.168.0.0/24)
WG Client access to only lan without Internet throw VPS.
All work fine on wan ! But when wan down and up wanb ping 10.66.66.1 
100% lost but lan clients is going to the internet normal.
When i disable wan interface ping 10.66.66.1  ok on wanb.

Output of "ip route list table 1-250"
Table 1:
default via 172.17.165.1 dev eth0.2 metric 10
10.66.66.0/24 dev wg proto static scope link
172.17.165.0/24 dev eth0.2 proto static scope link metric 10
192.168.0.0/24 dev br-lan proto kernel scope link src 192.168.0.1
192.168.8.0/24 dev eth2 proto static scope link metric 20
212.x.x.x via 192.168.8.1 dev eth2 proto static metric 20
Table 2:
default via 192.168.8.1 dev eth2 metric 20
10.66.66.0/24 dev wg proto static scope link
172.17.165.0/24 dev eth0.2 proto static scope link metric 10
192.168.0.0/24 dev br-lan proto kernel scope link src 192.168.0.1
192.168.8.0/24 dev eth2 proto static scope link metric 20
212.x.x.x via 192.168.8.1 dev eth2 proto static metric 20