I installed macOS 10.12 GM (16A320) on my 2 Macs (a late-2012 Mac Mini and a 2015 Retina MBP). Both machines are signed in to the same iCloud account. The Mac Mini which is at home typically has my NAS mounted via smb.
A new problem that has appeared is this:
On the laptop, when logging in, the SMB "connect-to-server" dialog will pop up, attempting to access the NAS. This happens even when I am not connected to my home WiFi network. I usually just cancel this, but it continues to pop up throughout the session (usually when open/save dialogs are triggered).
Has anyone else experienced this behavior or know how to prevent it? I've been using these 2 Macs since 10.10 and never had this happen before.
edit: So I figured out what was causing this. I store my iTunes music library on the NAS so that I can access the same library from both of my computers. This never caused an issue before, but apparently iTunes 12.5 and/or Sierra handle this differently. They attempt to scan or interact with the library immediately upon login and then continuously throughout your session. So, if you have the library stored on external media or an SMB share as I did, you'll be constantly nagged to mount the volume. I couldn't figure out how to stop this bad behavior, so I resorted to simply deleting my iTunes library from the laptop for now.