ADVPN Spoke-to-Spoke Communication Failure When Hub is Down

We are currently facing an issue in our ADVPN setup. Whenever the hub firewall goes down, the following problems occur:

BGP sessions drop and all routes are withdrawn.

Spoke-to-spoke shortcut tunnels remain in the UP state, however spoke-to-spoke communication does not work.

Our expectation from ADVPN was that spoke-to-spoke tunnels should continue to operate even if the hub is unavailable. However, in our case everything depends on the hub.

Could you please confirm if this is a design limitation or if there is a configuration/workaround to maintain BGP routes and spoke-to-spoke communication independently of the hub? Kindly guide us with the best practice solution.