Offline viewing over SMB not possible?

The other day my ISP had a maintenance so internet was down. No problem I thought, I’ll just connect through SMB on my NAS and watch the files locally instead of the usual Plex library connection. I was able to successfully connect to and browse all my files but when pressing play, all I got was a spinning circle. The connection is Ethernet for both ATV and NAS and they are obviously able to talk to each other. Am I missing something here or shouldn’t I be able to play files locally?

Should be no problem if everything is configured correctly, I play only from my NAS too.