Update, 20201014: Just received validation (see comment from "Blackbird") that this solution continues to work in 20.04. Thanks Blackbird for the useful feedback!
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-