what(): Spinnaker: Can't clear a camera because something still holds a reference to the camera [-1004]
The web site was restructered so the link is now https://www.flir.com/support-center/iis/machine-vision/application-note/understanding-usbfs-on-linux/ basically it is saying to either set it in /etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash usbcore.usbfs_memory_mb=1000"
and then update grub with sudo update-grubor to use following command
$ sudo sh -c 'echo 1000 > /sys/module/usbcore/parameters/usbfs_memory_mb'
For me on 18.04.2 LTS the first way worked well.