On Windows only, operations fail using ssh with PKI

I am updating code that was previously Linux-only to support Windows, and my tests are failing on Windows with errors like

ERROR: Cmd('git') failed due to: exit code(128)
  cmdline: git clone -v -- ssh://<redacted> C:\Users\stevjorg\AppData\Local\Temp\clitest-qevu7qrx
  stderr: 'Cloning into 'C:\Users\stevjorg\AppData\Local\Temp\clitest-qevu7qrx'...
Permission denied, please try again.
Permission denied, please try again.
<redacted>: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

I can successfully execute the same command that is shown for "cmdline:" manually at the Windows command prompt.

The connection uses ssh keys, so no password is used/needed.

Any ideas?