If your RDSH server and the license server are domain joined and you are using RDS User CAL, the user that log on the RDSH server has to be a Domain user because the license server will try to write the RDS license information in the user account attributes.
If the user is a local user, it's the same thing as a "workgroup" and RDS User CAL does not support workgroup environment and the license server will not be able to assign a license so the user will be "unlicensed".
Windows server 2019 has a new behavior for unlicensed users and it will disconnect users every 60 minutes.
If you want to use local users and not Domain users, you will need to use Device CAL instead of User CAL.
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