Some of your channel power levels are borderline out of spec and are above 10. I'm not saying this is the issue but could be contributing to it. Mine sometimes goes to 11, but I dont really have many if any issues, possibly a reduction in speed to 850.
It will probably need a engineer visit to fix this. Maybe post your upload channel power info as well, as that can effect download speeds.
Also getting errors on some of your download channels? Id try a pin reset and make sure cable connections are tight.
Maybe check to see if any local area faults.