We are experiencing issues with several of our feature layers in map viewer and web applications.
When the layer is loaded, it only shows parts of it and there are other parts missing (looks like tiles, but this is a simple feature layer - see below).

When I zoom in and out, some of the missing parts might appear, but others disappear

I do not see any errors neither in ArcGIS Server manager, nor the browser console.
The behavior is the same in different browsers. It happens with many different feature layers.
Any ideas where this is coming from and what can be done against it?
We are working with ArcGIS Enterprise 11.3.
The feature layer data comes from SDE databases.