There are 8 predefined traces in ArcGIS Pro 2.5 for UN:
Connected, Subnetwork, Subnetwork Controllers, Upstream, Downstream, Loops, Shortest Path and Isolation. They were all differently defined in Pro 2.5 for use with the UN. I use Subnetwork all time as I am presently converting our Geometric Water Network to UN and creating our low/high pressure zones in the Water Distribution Utility Network Foundation. As soon as I loaded ArcGIS Pro 2.6 they are still available but have all changed to the same generic Trace Pane. For example Subnetwork had predefined barriers such as closed valves, etc.
Hope I explained that correctly (I am bad on terminology in UN), wondering if anyone else has seen the same. I'll probably have to put a ticket in for it after the long weekend here, working a bit from home.