Or your router isn't responding correctly to traffic controls or the ISP isn't sending them correctly? I know with one provider I had in the deep past the allowable packet size was smaller than what most devices default to and they weren't correctly sending the maximum size their routers supported in the appropriate ICMP requests. Eventually I figured out that I could force my router to a smaller allowed packet size and that at least decreased packet loss substantially going upstream, even if whatever misconfiguration of the ISP was still confusing and eating downstream packets.