Hey, if you're still facing the issue, then please turn out to the feedback section for help.
Kindly follow the steps as below to report an error on the feedback section.
Log in Samsung Members app > Click “+ button” at the bottom right > Click “Send feedback” > Click “Error reports” > Add detail of symptom and attach the system log data (click checkbox)
*When you abstract the log file. Please check off the pop-up message: log file delivered
You can also check this link which explains in detail the entire steps to send feedback: https://r2.community.samsung.com/t5/Community-Guidelines/Send-Feedback-Report-a-Bug-to-Samsung/m-p/3...
To me this was not an issue before the update made to Windows Smart Switch app May 2020. Now I am also getting this Error message from Smart Switch. The problem is that Dex is not exiting as far as Windows is concerned even though the Dex windows closes. Dex continues to run as a background task. If you run Task Manager (Ctrl-Alt_Del) and scroll down the Background Processes you will see Samsung Dex listed. Select it and click End Task and it is then shut down. Smart Switch will now work correctly.