Thanks for reaching our forum and would like to confirm some details to understand your issue better.
1.Is there any message prompted before the user session been disconnected randomly?
2.As you mentioned currently the issue only occurred for one user, did he/she tested by using another client PC to remote the target one?
3.Please also take a look at in both side of the computer around the timestamp of disconnection in the event logs and verify if any abnormal information occurred.
Event Viewer-Windows Logs-Security
Event Viewer-Windows Logs-System
Event Viewer-Applications and Services Logs-Microsoft-Windows-TerminalServices-RemoteConnectionManager/Operational
Event Viewer-Applications and Services Logs-Microsoft-Windows-TerminalServices-LocalSessionManager/Operational
For more details of Event ID, please refer to below link.
Windows RDP-Related Event Logs: Identification, Tracking, and Investigation
For disconnect codes, please refer to below link.
RDS Session Host Server Disconnect Codes
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