I experience inexplicable and inconsistent downstream trace results. I have really tried myself understanding what is going on - I do not get it though.
From a high voltage substation (HV/MV) I set a trace start flag on the secondary winding on one of the transformers and request a downstream trace - se screen dump below:

As the trace is set to continue into low voltage (target tier), of course I would expect the trace to do so. In the below screen dump, you see that it does not continue into the low voltage mesh (blue lines):

And zooming into a medium voltage substation (MV/LV) it is clear that the trace stops at the MV/LV transformer - se screen shot below:

Really strange, cause I have successfully run an update subnetworks on the low voltage mesh, so I know that the trace from this transformer and downstream should work.
Now, moving the trace start point (from the HV/MV transformer secondary) to just outside this substation and running the exact same trace I reach this inconsistent result that you see below - the trace continuing through the MV/LV transformer and into the low voltage mesh as configured in the GP:

Enlighten me please, Esri (or someone else). I cannot see me doing anything wrong here - I might though. Or UN might have a bug?
One thing is for sure - you have a puzzled user.