I am sorry I don't have any answers, but I am experiencing intermittent outages as well, but they don't seem to last as long as yours. One of the things I would like to do is track how often and for how long I am having problems. I saw the modem log you attached. Is that the only way to get what I am after. Those messages are pretty cryptic. I was hoping for something that was a little more intuitive.
Note, I have yet to contact Xfinity about the issue mainly because I did not want to go through the same isuues you have experienced. Most of the time it works, so I am sure when a technician came out, it would be working fine. I don't want to waste a bunch of time on this so I thought I would start with collecting the data.
Thanks and good luck figuring out your issue. I know that can be frustrating.