This reference seems to be authoritative on disabling usb autosuspend.
Although the USB autosuspend is a feature designed to preserve battery life, its' 18.04 default is "enabled", whether or not the device Ubuntu is being installed on even has a battery.
Further, in order for autosuspend to be more help than harm, it appears that the USB device's driver needs to support autosuspend. Hence all the posts- yours' included- seeking to disable the "feature".
In 18.04 on my device, I scripted disabling autosuspend persistently in
/etc/default/grub like so:
sed -i 's/GRUB_CMDLINE_LINUX_DEFAULT="/&usbcore.autosuspend=-1 /' /etc/default/grub
sed expression just prepends "usbcore.autosuspend=-1" with a trailing space after the initial quote mark to ensure it always matches whatever your particular GRUB_CMDLINE_LINUX_DEFAULT options look like.
If you execute
cat /sys/module/usbcore/parameters/autosuspend after a reboot, you'll remark the "-1" preference (disabled) is retained.
Anyhoo, hope this helped you out-