Comment 14 for bug 1915511

This looks like agents can't reach the new controller. Have you ensured that the new controller is on the same network(s) as the original controller and reachable/pingable from all units within the network?

Oddly, the logs don't seem to show what API address is being attempted for the "target controller", unless all of the connected to upstream API is correct and what you actually have is a new-model hung controller not willing to provide data to the endpoints.

2021-02-22 08:06:30 ERROR juju.worker.migrationminion worker.go:197 validation failed: failed to open API to target controller: try again (try again)