It's an on-prem CVAD integration scenario with StoreFront Cloud
In the first logon attempt, user authentication and resource enumeration take nearly 2 minutes after entering credentials.
However, the consequent logon attempts are a bit faster compared to the first attempt.
Unreachable sites are added to StoreFront Cloud which caused timeout error during enumeration.
In StoreFront Cloud, disable on-premise DDC sites which are un-reachable.
In StoreFront Cloud, one or more on-premises CVAD sites has been added (site aggregation).