Where are user's SSH keys stored by the internal SSH server when running on Windows

When users enter an SSH key into their profile, where are they stored?
SHH connections using those keys are failing to authenticate and I can’t see the keys being written out to the filesystem anywhere.

It may be a permissions issue on the filesystem and I need to know where they should be stored to address that.

More general question with details of configuration here; Publickey error using internal SSH server on Windows server