I will open a defect around this item and associate you to it. Would it be possible to have you send me the diagnostics so I can attach them to the defect for the Dev guys to track down the issue?
So you may want to try this, I cannot guarentee it would work, but might be a workaround. With 9.5 we changed the discovery engine, however, still ship with the old discovery engine which you can navigate to the exe and run manually. Mine is here and called netperfmondiscovery.exe (C:\Program Files\Solarwinds\Orion). Importing from here may not truncate the hostname.
Also, not sure if you are on SP4 or not, but with SP4 we made some tweaks to web node management to increase performance which have received good feedback on, there is another thread on this is you want to see it.
I just renamed the nodes with the database manager one by one.
For future import tries, is there a way to disable subnet scanning? I want to give orion an exact list of only these routers to import and nothing else.