If a large number of files are moved using the drag & drop feature, it is very likely that some will get permanently deleted in the process. This is due to the Destroy routine being initiated before the Create routine has completed. Using the demo page here https://demos.telerik.com/aspnet-mvc/filemanager I've been able to replicate the loss of files. Steps are simply:
Almost immediately, you will find there's no longer 10 images as the Create routine fails to complete before the Destroy routine is initiated resulting in 1 or more files being lost. With very little effort, I was able to reduce the 10 images down to 6 - I would class this as critical.
After 1 move operation, the 10 files are now just 8: