I've been dealing with Xfinity on the phone and online and seem to be dealing with folks who don't understand the issue, so they give me routine try-this and try-that advice. I'm trying to figure out if a tech needs to come out or if there's anything I can do. The issues have come up after Xfinity emailed me to suggest I upgrade my modem to one on their current approved list in order to get the 400 Mbps my plan now provides. I did as suggested and ever since have had problems that get better and worse. Sometimes I get 400+ but other times the speed is down in the single digits and regularly I get T-3 Timeout and MDD Timeout warnings. Had lower high speeds with the prior modem (Netgear C3700) but the problems occur only now with the newer one (Moto MB7621).  Here's the Downstream Ch. Data. The high Uncorrected on 21 and 22 happens regularly and I don't know if this is a red flag.

Downstream Bonded Channels

Channel Lock Status Modulation Channel ID Freq. (MHz) Pwr (dBmV) SNR (dB) Corrected Uncorrected 1 Locked QAM256 21 525.0 1.5 0.0 6273 411 2 Locked QAM256 1 399.0 -4.3 40.8 0 0 3 Locked QAM256 2 405.0 -2.5 42.1 0 0 4 Locked QAM256 3 411.0 -1.9 42.8 0 0 5 Locked QAM256 4 417.0 -2.1 42.6 0 0 6 Locked QAM256 6 429.0 -0.9 43.4 0 0 7 Locked QAM256 7 435.0 -0.9 43.3 13 0 8 Locked QAM256 8 441.0 -0.4 43.5 0 0 9 Locked QAM256 9 447.0 -1.0 41.9 0 0 10 Locked QAM256 10 453.0 -0.5 41.4 377 583 11 Locked QAM256 11 459.0 -0.8 43.1 0 0 12 Locked QAM256 12 465.0 -0.2 43.0 0 0 13 Locked QAM256 13 471.0 -0.6 39.5 0 0 14 Locked QAM256 14 477.0 -0.1 43.3 0 0 15 Locked QAM256 15 483.0 -0.4 39.2 0 0 16 Locked QAM256 16 489.0 0.4 42.5 0 0 17 Locked QAM256 17 495.0 0.0 42.9 0 0 18 Locked QAM256 18 507.0 0.2 43.5 0 0 19 Locked QAM256 19 513.0 0.6 38.9 0 0 20 Locked QAM256 20 519.0 0.0 34.0 344 0 21 Locked QAM256 5 423.0 -1.9 44.0 6332661 5301225 22 Locked QAM256 22 531.0 0.1 26.4 7084814 6291016 23 Locked QAM256 23 537.0 1.1 36.5 0 0 24 Locked QAM256 24 543.0 0.6 31.5 13433 2 Total             13437915 11593237