If you set args.IsCancelled=true in any CUD event handler, the loading sign will never go away.

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ADMIN EDIT

If you don't need to cancel the event (e.g., because remote validation or data operation failed), you should avoid cancelling it - its purpose is to keep the grid in the current mode (edit/insert) when the operation fails so the user does not lose data.

That said, the loading sing should disappear in thsoe cases too, and a workaround is to disable it by setting the EnableLoaderContainer="false" parameter of the grid.

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