If a query returns a large dataset, the whole dashboard will freeze in an attempt to render the widgets.
Unsure if this is related so let me know if I should make a new ticket. However I have found if previewing a query that returns a large dataset it will return "Query preview failed with the error: An unexpected server error occurred.". It seems to give this error for queries that return an estimated 200-300 rows or greater.
I have also noticed in some cases this will freeze other dashboards I have access to, and then come good again in a few minutes.
Customer support service by UserEcho