This is another one of these random validate network topo failing with a cryptic message. There will be nothing in server logs to try and track this down. I'd suggest submitting a ticket to support even if you get it working. They are using our tickets like these to hopefully make things better for future releases. I will say 10.8.1 and Pro 2.7 are much better than 10.6 and 10.7 and we've seen less of these errors and the ability to recover from these errors improve.
Are you using the tool in ArcToolbox?
No, just in the Utility Network Data tab
do you get the same message with the tool?
you might get a better message if there is an error or incomplete step in the process
This is another one of these random validate network topo failing with a cryptic message. There will be nothing in server logs to try and track this down. I'd suggest submitting a ticket to support even if you get it working. They are using our tickets like these to hopefully make things better for future releases. I will say 10.8.1 and Pro 2.7 are much better than 10.6 and 10.7 and we've seen less of these errors and the ability to recover from these errors improve.