I met some people who had the same problem.
If this is the reason for the copy paste not to work, the quick solution is to restart the rdpclip.exe program in the remote computer.
Here are the steps:
1.Kill the process rdpclip.exe using the task manager in the remote computer
2.Go to RUN command and start the application rdpclip.exe
I consider that you could update ( such as Remote desktop app).
Hope this helps and please help to accept as Answer if the response is useful.