network shares - Virtualbox - folder does not automatically mount, Windows 7 host Ubuntu 17.10 guest

I'm trying to use Virtualbox's shared folder functionality, and I can't get the automount folder feature to work.

I've followed directions in various SO/AskUbuntu questions, and it seems like I set up shared folders correctly.

More details:

Mounting the folder with sudo mount -t vboxsf vbox_shared /media/vbox_shared works, including write access.

I've installed Virtualbox Guest Additions, and lsmod | grep vboxguest returns vboxguest 294912 2 vboxsf,vboxvideo.

I've run sudo usermod -G vboxsf -a to add myself to the group.

I've restarted the virtual machine.

In Virtualbox settings, I've set Folder Path: C:\Users\\vbox_shared, Folder Name: vbox_shared, Auto-mount and Make Permanent are checked.

Host is Windows 7 Enterprise, Guest is Ubuntu Server 17.10, Virtualbox 5.2.6.

What else could be the cause of this?