I have been using the utility network analyst to trace path and to find disconnected NHD streams in a HUC4. Recently, all possible choices for tracing a network in the Utility Network Analyst toolbar are not working. I can set a flag but no actions result when I click on the solve tool. I am working in 10.7
Cross-posting this to Geodatabase since this question is centered on the Utility Network Analyst toolbar in ArcMap with the geometric network and not the Utility Network.
Do I understand that you are not seeing any results returned when running a trace in the geometric network? Are you seeing the same behavior when you return the trace results as a graphic (or as a selection)? Is this behavior seen when working with the same data in a new MXD? What about when you attempt to trace other datasets? I've seen behavior similar to that you reference linked with a specific MXD in the past.
I'm experiencing the same issue, but only when the results are set to 'selection'. It works when I have the results output to a drawing. But I cannot figure out how to export those results to a separate layer/shapefile.
I believe I figured it out. Looks like when I installed 10.7 and then 10.8, the interactive selection method, by default, was set to 'select from current selection'. I changed that to 'create new selection' and voila! You can find that setting under your 'Selection' menu > 'Interactive Selection Method'.
Hope this helps