You might experiencing a problem with an old, previous shotcut.exe process that did not close as described here:
That can also explain why you are unable to delete a file because the old shotcut.exe process still has it open, and Windows will not let you delete it.
Close Shotcut if running, open the Task Manager, go to Details, look for shotcut.exe, select it, and click End task.
Now, try deleting your files and see if the performance of Shotcut improves.