I am using WAB 2.8 on Portal 10.6.1. Related records do not show up in the Attribute Table widget. This is I believe related to an ArcGIS Online bug 'bug-000114004', which was fixed for ArcGIS Online, but apparently not for Portal 10.6.1.
Is there a work-around available for this problem? I am using Dev Edition as well, version 2.8, and I assume that I am bound to using 2.8 dev edition as long as I have Portal 10.6.1.
The error in console is 'no activeLayerInfo!, in the _getQueryTableInfo function in the Widget.js of the WAB Attribute Table.