I have a Scrum Board that tracks about 450 items. I can generate a burndown chart on my Jira dashboard for this Scrum Board with no problem. But when I use the "Sprint Burndown Chart" gadget on my Confluence page and use the same Scrum Board, the chart is blank. It does not show the graph - just the name of the Board. There is no error either. Please see the screenshot below.
On the same Confluence page, I am able to insert a Burndown Chart from another Board which has may be 50 Jira items.
My question, is there a limitation on this gadget regarding the Size of the Scrum Board?
Any help will be greatly appreciated.

Thank you.