Hello,
Upgrading the RUT device firmware will not upgrade the current modem firmware it is using unless you manually update the modem firmware to the latest one. For the link you shared in this question i was not able to receive any feedback on the client side anymore so maybe upgrading the device via boot loader mode solves the issue.
It is suggested to upgrade the firmware of the devices to the latest one to have the latest revisions and fixes made for the device.
Hope it helps
Regards,
Jerome