OK, if these issues are independent of your own router, maybe your ISP is at "fault" here maybe try one of the cake-autorate or sqm-autorate approaches that adaptively set the shaper limits to minimize latency under load... Because a static/fixed SQM configuration will only work if the true achievable rate through the ISP's network is >= the configured traffic shaper rate... if that is not the case than bufferbloat in your ISP's network will result in noticeable delay spikes on your side.