The rotating Circle which I am not getting here at all is usually caused by the following and is not related in anyway to N3V doing anything to your install other than maybe a server login issue causing repeated login attempts. check the log.
Database being cached after downloading a lot of assets or new DLC from manage content.
Database being cached after doing a database repair, disk activity can continue after Manage Content has finished the DBR see screen shot below.
Database doing a repair due to a bad shutdown or crash.
AV doing a scan if Trainz not excluded.
Antimalware doing a scan if Trainz not excluded.
Windows search indexing any new or changed files, disable it on Trainz folders.
This was disk activity in Resource Monitor 5 minutes after a Database Repair had finished, think this is due to disk caching updating the MFT and such as I have indexing and on access paranoia scanning disabled for Trainz folders, always worth checking if you have been doing a lot, that disk activity has actually finished before shutting down Windows which has a mind of it's own.