An ECS providing SNAT must have Unbind IP from MAC enabled.
The destination of each route in a route table must be unique. The next hop must be a private IP address or a virtual IP address in the VPC. Otherwise, the route table will not take effect.
If a virtual IP address is set to be the next hop in a route, EIPs bound with the virtual IP address in the VPC will become invalid.

Are There Any Restrictions on Using a Route Table?