I see strange rendering artifacts when I use FeatureLayer with Multipoints and PictureMarkers. Here is a codepen to reproduce this problem: https://codepen.io/parshin/pen/ExPYBLp?editors=1000
After these changes, I see the strange artifacts on the map:
Both Multipoints and PictureMarker are required to reproduce this problem. When you zoom in/out the map, the artifacts appear in different places (the top-left corner of internal rendering tile?).
Is it a bug? Is there any workaround to remove this rendering problem?
Environment: ArcGIS JS API 4.15, Chrome, Ubuntu.
I am able to reproduce the issue you described. We have created an issue for this and will let you know as soon it is fixed. In meantime, you can use graphicsLayer with multipoint geometries.