@9960_user 

 

Enabling of bandwidth controls of any type (even when not applied) has a hardware overhead on the device, basically it takes compuation time and this can on occasion affect the overall performance.   Not saying this is the issue, but seen it before

 

This device is a much older model now, its likely got a slower chipset and less memory available so may suffer from the effects of bandwidth controls more.  

Well, my download speed is way lower than the maximum speed of this modem, so I doubt it's a hardware issue. I ran further test and noticed this speed drop only occurs if I set the "Line Type" as "DSL" in the Bandwidth control tab, but if I choose "Other", this problem wont occur, while I'm still able to apply my rules, specially for guest network. Another weird behavior is that normally I get the 350ms download ping (60 ms idle ping) in speedtest website, but if I enable the Bandwidth control in "DSL", my download ping decreases to 60. So overall I'm convinced 9960 modem has a software bug in allocating hardware resources.

  @9960_user 

 

It does sound like a strange symptom, so yeah it could be a bug in the feature

 

Sadly however as the device was end of life back in 2018 its almost guaranteed it wont see any further firmware updates.

  @Philbert 

My hardware is v1.2 with latest fw update of 2022-08-18.