High uncorrectables on three channels; High incidence of packet loss as a result

For the past few weeks, I have been dealing with interrmittent periods of heavy packet loss. Given that it came and went, I wondered if it might be a wifi interference issue or a router issue; however after checking a number of other potential causes I noticed that three channels are showing significant amounts of corrected and uncorrectables on downstream in the modem's log.. This issue seems to persist on the same channels even after modem resets. The strangest factor is that the interference is completely random-we can have days of perfectly functional internet, then suddenly packet loss so severe it makes online gaming and video streaming impossible.

Yes, I have checked the coax connection to the modem (a single cable routed directly into our apartment through the floor near a wall) so I'm assuming the problem here is somewhere outside? This wouldn't be due to a failing modem, correct?

These are the readings only about 10-20 minutes after a reset:

EDIT: Picture isn't showing up, so here's a more recent reading: