Running gnome-boxes gives the following error

(gnome-boxes:6605): Gtk-WARNING **: Theme parsing error: gtk-style.css:76:18:
The 'outline-radius' property has been renamed to '-gtk-outline-radius'

(gnome-boxes:6605): Gtk-WARNING **: Theme parsing error: gtk-style.css:87:18:
The 'outline-radius' property has been renamed to '-gtk-outline-radius'

** (gnome-boxes:6605): WARNING **: Entity
http://download.opensuse.org/tumbleweed/repo referenced but not defined

** (gnome-boxes:6605): WARNING **: Entity
http://www.linux-usb.org/usb.ids/80ee/0021 referenced but not defined

** (gnome-boxes:6605): WARNING **: Using a file
(/usr/share/gnome-boxes/gnome-boxes-logos-db.xml) as a database location is
deprecated, use a directory instead

(gnome-boxes:6605): Boxes-WARNING **: machine.vala:606: Failed to start
openSUSE Tumbleweed: Unable to start domain: internal error: process exited
while connecting to monitor: at.spice.0 -device usb-tablet,id=input0 -device
usb-mouse,id=input1 -device usb-kbd,id=input2 -spice
port=0,disable-ticketing,image-compression=off,seamless-migration=on -device
qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vram64_size_mb=0,vgamem_mb=16,max_outputs=1,bus=pci.0,addr=0x2
-device AC97,id=sound0,bus=pci.0,addr=0x4 -chardev
spicevmc,id=charredir0,name=usbredir -device
usb-redir,chardev=charredir0,id=redir0 -chardev
spicevmc,id=charredir1,name=usbredir -device
usb-redir,chardev=charredir1,id=redir1 -chardev
spicevmc,id=charredir2,name=usbredir -device
usb-redir,chardev=charredir2,id=redir2 -chardev
spicevmc,id=charredir3,name=usbredir -device
usb-redir,chardev=charredir3,id=redir3 -device
virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x7 -msg timestamp=on
spice-qemu-char: unsupported type: smartcard
allowed names: vdagent, usbredir
qemu-system-x86_64: qemu-char.c:4533: qmp_chardev_add: Assertion `!i' failed.

This is on Leap 42.2 with all the latest updates. This is my gnome-boxes
version:

oweinerlab@null-c82a1447f5bc:~> zypper info gnome-boxes
Loading repository data...
Reading installed packages...


Information for package gnome-boxes:
------------------------------------
Repository     : Main Repository (OSS)                                          
Name           : gnome-boxes                                                    
Version        : 3.20.2-2.1                                                     
Arch           : x86_64                                                         
Vendor         : openSUSE                                                       
Installed Size : 2.9 MiB                                                        
Installed      : Yes                                                            
Status         : up-to-date                                                     
Summary        : A simple GNOME 3 application to access remote or virtual
systems
Description    :                                                                
    Boxes is an application to easily create, setup, access, and use: remote
    machines, remote and local virtual machines, and, when technology permits,
    applications on local virtual machines.

oweinerlab@null-c82a1447f5bc:~> 

https://bugzilla.opensuse.org/show_bug.cgi?id=1007263 looks related