I and others at my client site have experienced the same issue, it's either a QS bug or a browser issue.
Are you using QS Server or desktop ? Our issue is at the Server development level.
In the end the fix is abort the session and open a new one. In theory your sheet should be saved at least
up to the point when you started moving the object around.
Not an answer really, but you are not alone with the issue, perhaps Qlik could look into this.