We only have one report of this in the SR history and it was a broken install. Without logs or any other information about the situation I would assume a permissions issue or an install that wasnt able to create files or registry entries that it needed. If not that then maybe another program on the machine that is holding this information and we arent able to get it.
you can see the last used credential provider in the registry here:
You can see all available credential providers here:
Are other installs working fine?