Yes, I would agree that also adding the old NAS would be a good test here to see if this is more networking-related or just localized to that specific test. You can feel free to move your current Roon subscription between as many Cores as you’d like, but I won’t be able to provide an additional license.
When you move the Roon Core, it will ask you to un-authorize the previous one and this is a relatively straight-froward process. I would suggest making a Backup of your Roon database before switching Cores though.
Please do let me know the results of this test and some timestamps if possible.
Thanks,
Noris