Dataflow gen2 error: Something went wrong while loading required resources.

EDIT 2: Okay, I refreshed my browser and the fix I describe below works again. 

EDIT: I jumped the gun - this definitely fixed my issue for a very short period, while I wrote this post essentially. But now the error is back? 

Helllo Anonymous and Pieter_NL,

I was initially replying here to echo the error that was posted. I was getting the same error and could not find much useful information so I hope this is helpful. I had the "ConnectionsInScope" error for most data sources like SQL Server and Sharepoint, but when I tried importing an Excel Workbook, I had a much more violent error that I found described in this post (link to similar post w/ solution).

Credit to user PaulHayes in that thread for discovering (or at least posting) that enabling the Gen1 Dataflow setting in the Admin Portal solves our issue. It appears that you need Gen1 dataflows enabled to use Gen2 dataflows. That makes mixed sense to me - but when I enabled this I no longer had issues connecting to datasources in Gen2 dataflows. 

Hope this helps you and others.