In ArGIS Web AppBuilder, services such as feature services and map services can be added to the map via the Add Data widget. However, these services may take a long time to load data in the web app, especially when compared to the loading times of the same services in ArcGIS Online or Portal for ArcGIS Map Viewer.
This issue occurs in services containing a large amounts of features, and when a sizable amount of users are attempting to access the web app containing the feature service. In these cases, the service in question can be assigned with a higher number of instances, which is useful in pooling a higher amount of system resources, such as physical memory (RAM) and CPU cores towards the service. However, increasing the number of instances to a point where it exceeds the amount of resources available also causes an overall reduction in system performance, thus increasing load times in web apps.
To summarize, the following are reasons why services may take time to load on a map in a web app:
The following are best practices to improve service performance in web apps.