This old friend has started to appear again. As usual there's no XD open or found to be active in any background process in Windows. As usual rebooting Windows does not help. I have NO Adobe application open. There are NO Adobe applications active in the task manager. It's about time someone in the Adobe XD team took a long hard look at this issue.
We're so sorry to hear about the trouble. Usually, this message stops popping in once Adobe XD process has been terminated. In case if you are still getting this message even after terminating the XD process from the Task Manager/Activity monitor, please try to close processes by following the steps shared here: https://helpx.adobe.com/download-install/kb/close-conflicting-processes.html