hi John I'm using a Mac mini so not sure how to put into safe mode though I've put the superb into modem mode and it finally connected after switching between connected not connected and self assigned ip a few times. the few speed tests I have managed to run are showing full speed down and up.
though not sure why I'm getting these random speed drops as I have had the same devices on the network before it started. that would be a tivo v6 box a Mac mini (main computer) two iPads a Synology nas and a xbox one x none of which are downloading anything while the speed tests are run and at times theres only the Mac been plugged in so as to rule out the other devices causing problems.
Thanks for the update Patrick, I'v been running dome historic checks on your cable segment and can see that there have been periods of low SNR and high FEC count which sounds like it could be the trouble.
If problems recur could you please drop us the date and time so we can cross check this against our network data and get it raised if needed.