There is an issue, when Software flow offloading option is enabled in Network -> Firewall -> General settings (which is enabled by default in 7.4). Mobile data limit feature will not work as sent/received data will not be calculated. Since this is a serious flaw in cases, where mobile consumption is relevant, firmware was removed. This applies to RUTX, RUT9M and RUT2M series devices.
Current workaround would simply be to disable Software flow offloading in 7.04.
Developers are working to find a proper solution, where flow offloading could be implemented without compromising data monitoring.
Apologies for the inconveniences.