An orange exclamation point appearing at the top-right of your viewlet is a warning. Hover over the icon to view the warning message. Usually this message means that not all data from the back end was retrieved.
In the example below, the number of generated chart graphs is limited to 100. The warning message, Drawing first  out of  graphs, is displayed. It is alerting you that there are more than 100 graphs.
The warning message can contain multiple alerts.