Just a gotcha in case anyone else bangs their head against the wall for this. If you are using a mosaic dataset and setting the order by attribute with a date field. Make sure that the order base value is at the temporal resolution of your date values. I had 5cm and 10cm data that was collected a couple days apart, the 5cm was the most recent. I store the collection in a date field, and to a day's resolutin (i.e. no time). I want the most recent image on top, no matter the resolution.
I had set the order base value to be 2100 (year 2100), and for the life of me I couldn't figure out why it was looking ok at some scales but when I zoomed in I had to muck around with the lowps/highps to get the right draw order.
Then I changed the order base value to 2100/01/01 and everything works correctly.
