If it does it again, do you have a separate network switch you could use to test it? I would create a small network with just one PC, a network switch and the NAS, and see how it acts on this small network just copying files between the NAS and PC. That should show if there is any issue directly with the NAS itself.

Also has anyone else online posted anything similar about this NAS causing these issues?

I'm personally still thinking it is an overheating or PSU issue with your current router/modem.