Apparently, the migrations assume that the old config secret must refer to a managed instance, even though specifying a current config secret (without anything else) implies an unmanaged instance. I apologize, I didn’t think it worked like that.
What I think you can do instead, is migrate the data yourself directly from crunchy to cnpg, and then spin up a new awx-cnpg instance with only the secrets it needs for the cnpg database (i.e. leave out old_postgres_configuration_secret). I have a detailed post relating to migrating data between two pods for a botched upgrade. You’ll have to fiddle with the targeted hosts, username, and passwords, but I think it should work. I had the luxury of being able to use the environment variables and re-using the same credentials between hosts.