Hi mpatilesriaustralia-com-au-esridist , thanks for pointing this out. There some significant changes to the utility network in 2.6 and we have not yet updated our foundation to include those changes. However, for now you can just remove the Utility Network Layer from the map and add it back, only it, not all UN layers, and everything should work correctly.
John Alsup
jalsup@esri.com