JumpCloud creates local user accounts on Windows hosts it manages, these hosts are not part of a domain.
When remotely logging into a non-domain host (for example, a JumpCloud-managed Windows system) from a host that is part of a Microsoft Active Directory domain, the remote desktop client will default to attempting to authenticate with the current domain. This results in a failure to login for all JumpCloud users on the JumpCloud-managed host. To login correctly, you'll need to specify no domain:
or the work group name of the host (which defaults to WORKGROUP), as in: