Unable to reproduce the issue with Portal for ArcGIS 10.5 and 10.5.1. Several improvements have been made beginning from Portal for ArcGIS 10.4.1 in terms of cache generation time and memory utilization. Please have the customer upgrade to latest software.
解决办法
Increase the maximum number of instances for scene caching tools or use the manage scene cache to rebuild specific layers after the service is published.