Does this occur for EVERY job you attempt to initiate for this particular Robot/Credential and Machine? Or occasionally?
Verify the credentials you are providing to the Unattended Robot including the format of the username <domain>\<username> As you didn’t specify if you were using a Domain Join Machine or Domain Credential vs Local
Are there any warnings when you RDP into the host manually with the same credentials such as an authorized user warning, etc.
An older KB, but covers some common scenarios I would go into depending on the above and symptoms you have and steps to reproduce.