Hello,
This is a known issue, as SQM/QoS was simply not implemented for the mobile interface, because it is quite a complex task.
Currently, it is planned to be added in v7.5 of RutOS, however, there is a good chance that it will get pushed further into the future.
For now, we recommend applying the needed rules to the br-lan interface instead of a mobile interface.
Best regards,
DaumantasG