The Incident Chart dashlet supports splitting over ten traffic lights. The 'Split Chart' option may have been disabled which may have caused your issue. If you right click on the chart and select 'Split Chart', please verify that the 'Split Chart' option is checked. I hope that helps!
Hmm, that's odd. I see that you created a support ticket, we may have to wait for a reply from a support engineer. I personally have not seen this behavior when the Split Chart option is selected.
I have been frustrated by this myself. I think the logic is that 10 is about the limit where the charts and legends are well sized when split, so it auto-switches to aggregated mode, but I think it just depends on the device and resolution if that is a good limit or not. Sometimes, like Spinal Tap, we may just want to go to 11. Anyhow, I just create multiple incident charts and put 10 or less per chart, then arrange them in rows or columns to work around this.
I am glad you opened a case, and am hoping there is a secret debug flag or something to help.
We found the same thing when going from DT AppMon 6.3 to 6.5 - the 10 limit was imposed at that time and we had to alter a few of our dashboards to make more 'rows' of dashlets under the 10 limit.