[ubuntu] 16.04 not prompting for updates on certain systems?

Hi friends. I'm working with two 16.04 systems. Both were 15.10 >> 16.04 upgrades. One is a laptop, one is a desktop.

With the desktop, I get a popup with update manager, telling me there's updates.
With the laptop, I get a notification (notify-send style bubble) telling me there's updates, but update manager does not automatically open.

Is this a setting somewhere I can control to make it do this behavior? With both systems previously on 15.10, both of them brought up the update manager. If it's a setting, I didn't set it, though I'd be curious to know.

Thanks for any insight!