When HTTP/2 is enabled on IIS, an influx of concurrent requests through the ArcGIS Web Adaptor (IIS) may result in server instability. To prevent this, the maximum number of concurrent requests per server is set to a default value of 150 as of ArcGIS Enterprise 12.0. This limit can be changed by updating the value of the maxConcurrentRequestsPerServer property in the WebAdaptor.config file, which by default is located in the C:\inetpub\wwwroot\<web adaptor name> folder.