I am having the same issues for about 10 days now or so, with occurrences being more frequent recently. I replaced the modem but the issues continue. T3 and T4 timeouts in the log at the moment of an outage. The connectivity restores within 3-4 minutes (I guess after the modem reset the cable interface and reconnect/re-register itself). Found that page: https://pickmymodem.com/cable-modem-t3-and-t4-timeouts-error-messages-and-how-to-fix-them/ but it's not clear what to do next. Talked 2 times with the Xfinity support but they have no clue what I am talking about, alas.