Faulty Feature service Visualization in Map Viewer (ArcGIS Online)

[Oana]

Hi! 

There are two things that I wish to clarify.

One one hand, the layer -in 1st image below- is a feature service published via ArcGIS Pro and opened with Map Viewer. The problem with it is when panning or zooming around the data is displayed very irregular (appears and disappears). This issues is only with the feature service, NOT if published as map image service (renders actually very well). Are there any parameters that have to be set in ArcGIS Manager Service or how can I solve the feature layer to render properly?

On the other hand, even though Map Image Service works well when visualizing the data, in the Layers pane -  in Map Viewer, there is a collapse button that show me twice the layer. Does anyone know if it is possible to get rid of the collapse button with two corresponding visibility icon? (2nd image below)

Also I am adding the layers with Rest API.

Thank you. 
I am not sure if I posted right, as I am new here. 

[RussRoberts]

What version of server are you publishing too? 

For the Map Image Layer the grouping is present when you add the MIL at the top level of the service. When you add it at the sub layer level it will be treated as a feature layer and appear as a single layer.

[Oana]

Indeed, MIL it is treated as a feature layer, but again the same issue with the data display when zooming in and out or panning. Could it be something with REST API, because when I add the MIL directly in the map is not problematic, and the feature layer is when added directly.
In order words MIL added directly works (but has the expand button), and when adding MIL as well as feature layer with REST API is faulty.

[Oana]

I am using Version 10.9.1

[PhilipWeeks]

I'm running into this and was curious if you found any more information on this.  This cluster should all be squared an aligned and they do on a closer zoom but further up it displays like this:

So it seems to be related to the detail a web map renders features at higher zooms so I'm really hoping there's a way to force it to render higher details and accept the performance hit.  Since a Map Image is rendered server side I'm guessing that's the reason it displays correctly.  If need be I can probably make things work with Map Image Services but it'd be nice to be able to clean up the layer list since a Map Image always come with it's own group.

It just really feels like I should be able to tell the client, "Hey, render this correctly instead of cheaply."