The Layer List widget in ArcGIS Web AppBuilder hosted on ArcGIS Online or Portal for ArcGIS shows all layers or nothing with each refresh when using a service with group and nested layers with the following option enabled, 'Allowing assignment of unique numeric IDs for Map Service Publishing.'
Last Published: March 11, 2016ArcGIS Online
Bug ID Number
November 21, 2015
September 22, 2022
Operating System Version
2008 R2 64 Bit
The bug has been fixed. See the Version Fixed and Additional Information, if applicable, for more information.