In my case the Vodafone router was ****. I changed to a Fritzbox... problem gone. The supplied router was forcing the line attn too low, 3.2db

. Now runs at 6db no problem.
Be careful about rebooting you router too often as this can make to cab think you have a poor line and for the DLM to increase error correction etc.
Have you measured your packetloss via Thinkbroadband BQM? Mine goes up and down all the time causing Netflix to become pixilated and drop quality from 4k. Gaming is not too good either

There's nothing I can do as it's a problem with ISP congestion.
Modem/router choice is like Marmite... some people love them.. most hate them

It's YMMV, I do know that my mates TP Link router (VR600) gave an unrealistic down load speed for the line length to the cab!! Even the Openreach tech had a doubts as it was more that her equipment measured..