I've had this happen a lot, though I can't yet tell exactly how to pin-point the reason for that.
Any indicator put on M1 TF, when playing a little with the chart (scroll back and forth, zoom in, zoom out) the indicator
finally disappears from portions of the screen.
Take for instance this case, with the PIVOT indicator just published on that site today.
I've attached to M1, played a bit and here's the result.
I think it happens to me also when I call an indicator from a script in M1 TF that sometimes,
the handle returned by ICUSTOM is ok, but the indicator buffers has zero values, although it is ok on the chart.