Two on-prem routers each have a VPN to a single Cloud Router. Each on-prem router uses a unique ASN, both have identical routes and priorities, BGP sessions are up, but only one router’s routes are installed. What is the most likely cause?

The most likely cause is that the ASNs being used on the on-premises routers are different. When multiple BGP sessions are established from different on-premises ASNs to a single Cloud Router, the Cloud Router, by default, prefers routes from only one of the ASNs to avoid routing loops and ensure consistent routing. Even with identical routes and priorities, the distinct ASNs cause this behavior. Incorrect options: The on-premises routers being configured with the same routes is expected and not an issue; it's the goal for redundancy. A firewall blocking traffic would typically prevent the BGP session from coming up at all, which is not the case here. A load balancer is for distributing application traffic, not for influencing BGP route selection on the Cloud Router.