Most likely your “box” is any kind of shape you may have created inadvertently, and which isn’t a member of the chart. Unfortunately general shapes and charts in Clac do not regard the ordinary Z-order when rendered, and the ordinary shape may show inside the area the chart is claiming even if none of the shapes is set to be transparent.
To check if my guess is correct:
-1- Select the chart object and move it to get direct access to the “box”.
-2- Verify that the “box” did not move.
If so:
-3a- Select the “box” and make sure nothing else is selected.
-4a- Delete the “box”.
-5a- Move the chart to the place where you want it to show.
If otherwise:
-3b- Try one step of ‘Ungroup’ from the context menu.
-4b- Select a single sheet cell first and restart with -1- then.
-Finally- Report your experiences by adding a comment to this answer.
If your document is behaving in a way clearly refuting my guess, I would need it attached to your question for further investigation. After your report to that effect I would see for enough “karma” in your records to get you allowed to make attachments.